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# Fourth (basic) lesson¶

## Aluminum, the bulk and the surface.¶

This lesson aims at showing how to get the following physical properties, for a metal, and for a surface:

• the total energy
• the lattice parameter
• the relaxation of surface atoms
• the surface energy

You will learn about the smearing of the Brillouin zone integration, and also a bit about preconditioning the SCF cycle.

This lesson should take about 1 hour and 30 minutes.

## 1 Total energy and lattice parameters at fixed smearing and k-point grid¶

Before beginning, you might consider to work in a different subdirectory as for lesson 1, 2 or 3. Why not “Work4”?

The file ~abinit/tests/tutorial/Input/tbase4_x.files lists the file names and root names. You can copy it in the Work4 directory (and change it, as usual). You can also copy the file ~abinit/tests/tutorial/Input/tbase4_1.in in Work4. This is your input file. You should edit it, read it carefully, and have a look at the following “new” input variables, and their explanation:

Note also the following:

1. You will work at fixed ecut (6Ha). It is implicit that in real life, you should do a convergence test with respect to ecut … Here, a suitable ecut is given to you. It will allow to obtain 0.2% relative accuracy on lattice parameters. Note that this is the softer pseudopotential of those that we have used until now: the 01h.pspgth for H needed 30 Ha (it was rather hard), the 14si.pspnc for Si needed 8 Ha.

2. The input variable diemac has been suppressed. Aluminum is a metal, and the default is tailored for that case.

When you have read the input file, you can run the code, as usual (it will take a few seconds). Then, read the output file quietly.
You should note that the Fermi energy and occupation numbers have been computed automatically:

 Fermi (or HOMO) energy (hartree) =   0.26847   Average Vxc (hartree)=  -0.34746
Eigenvalues (hartree) for nkpt=   2  k points:
kpt#   1, nband=  3, wtk=  0.75000, kpt= -0.2500  0.5000  0.0000 (reduced coord)
0.09425   0.25438   0.41909
occupation numbers for kpt#   1
2.00003   1.33307   0.00014
prteigrs : prtvol=0 or 1, do not print more k-points.

You should also note that the components of the total energy include an entropy term:

 Components of total free energy (in Hartree):

Kinetic energy  =  8.70954971782498E-01
Hartree energy  =  3.84986358590396E-03
XC energy       = -8.08434339502224E-01
Ewald energy    = -2.72948286712169E+00
PspCore energy  =  3.78721653637092E-02
Loc. psp. energy=  8.26684645838168E-02
NL   psp  energy=  4.52588269933839E-01
>>>>> Internal E= -2.08998347137414E+00

-kT*entropy     = -7.99729047978171E-03
>>>>>>>>> Etotal= -2.09798076185393E+00

Other information on the energy :
Total energy(eV)= -5.70889598417024E+01 ; Band energy (Ha)=   3.6059822203E-01

## 2 The convergence study with respect to k points¶

There is of course a convergence study associated to the sampling of the Brillouin zone. You should examine different grids, of increasing resolution. You might try the following series of grids:

  ngkpt1  2 2 2
ngkpt2  4 4 4
ngkpt3  6 6 6
ngkpt4  8 8 8

with the associated nkpt:

  nkpt1  2
nkpt2 10
nkpt3 28
nkpt4 60

The input file ~abinit/tests/tutorial/Input/tbase4_2.in is an example, while ~abinit/tests/tutorial/Refs/tbase4_2.out is a reference output file. The run might take about thirty seconds on a PC 3 GHz.

You will see that, for the particular value tsmear=0.05 Ha, the lattice parameter is already converged with nkpt=10:

            acell1     7.5588968086E+00  7.5588968086E+00  7.5588968086E+00 Bohr
acell2     7.5070431499E+00  7.5070431499E+00  7.5070431499E+00 Bohr
acell3     7.5016877756E+00  7.5016877756E+00  7.5016877756E+00 Bohr
acell4     7.4992662653E+00  7.4992662653E+00  7.4992662653E+00 Bohr

Note that there is usually a strong cross-convergence effect between the number of k points and the value of the broadening, tsmear.
The right procedure is: for each value of tsmear, to get the convergence with respect to the number of k points, then to compare the k-point converged values for different values of tsmear.

In what follows, we will restrict ourselves to the grids with nkpt=2, 10 and 28.

## 3 The convergence study with respect to both number of k points AND broadening factor (tsmear)¶

The theoretical convergence rate for tsmear ending to 0, in the case of occopt=4, is quartic. This is obtained in the hypothesis of infinitely dense k point grid. We will check the evolution of acell as a function of tsmear, for the following values of tsmear: 0.01, 0.02, 0.03 and 0.04. Use the double-loop capability of the multi-dataset mode, with the tsmear changes in the inner loop. This will saves CPU time, as the wavefunctions of the previous dataset will be excellent (no transfer to different k points).

The input file ~abinit/tests/tutorial/Input/tbase4_3.in is an example, while ~abinit/tests/tutorial/Refs/tbase4_3.out is a reference output file.

From the output file, here is the evolution of acell:

            acell11    7.5587661702E+00  7.5587661702E+00  7.5587661702E+00 Bohr
acell12    7.5587696944E+00  7.5587696944E+00  7.5587696944E+00 Bohr
acell13    7.5587696871E+00  7.5587696871E+00  7.5587696871E+00 Bohr
acell14    7.5587710578E+00  7.5587710578E+00  7.5587710578E+00 Bohr
acell21    7.5055168997E+00  7.5055168997E+00  7.5055168997E+00 Bohr
acell22    7.5056781966E+00  7.5056781966E+00  7.5056781966E+00 Bohr
acell23    7.5018335937E+00  7.5018335937E+00  7.5018335937E+00 Bohr
acell24    7.5041510220E+00  7.5041510220E+00  7.5041510220E+00 Bohr
acell31    7.4963466654E+00  7.4963466654E+00  7.4963466654E+00 Bohr
acell32    7.4957099831E+00  7.4957099831E+00  7.4957099831E+00 Bohr
acell33    7.4969520318E+00  7.4969520318E+00  7.4969520318E+00 Bohr
acell34    7.4993529673E+00  7.4993529673E+00  7.4993529673E+00 Bohr

These data should be analyzed properly.

For tsmear=0.01, the converged value, contained in acell31, must be compared to acell11 and acell21: between acell21 and acell31, the difference is below 0.2%. acell31 can be considered to be converged with respect to the number of k-points, at fixed tsmear.
This tsmear being the lowest one, it is usually the most difficult to converge, and the values acell31,32,33 and 34 are indeed well-converged with respect to the k-point number.
The use of the largest tsmear(=0.04), giving acell34, induces only a small error in the lattice parameter. For that particular value of tsmear, one can use the second k-point grid, giving acell24.

Summary

So to summarize: we can choose to work with a 10 k-point grid in the irreducible Brillouin zone, and the associated tsmear=0.04, with less than 0.1% error on the lattice parameter.
Note that this error due to the Brillouin zone sampling could add to the error due to the choice of ecut (that was mentioned previously to be on the order of 0.2%).

In what follows, we will stick to these values of ecut and tsmear, and try to use k-point grids with a similar resolution.

Our final value for the aluminum lattice parameter, in the LDA, using the 13al.981214.fhi pseudopotential, is thus 7.5041 Bohr. Note: for historical reasons (consistency with older versions of the tutorial), we will work on the following, with a slightly different value, of 7.5056 Bohr, that is 3.9718 Angstrom.
The experimental value at 25 degree Celsius is 4.04958 Angstrom.

The associated total energy and accuracy can be deduced from

           etotal11   -2.0916027819E+00
etotal12   -2.0931968906E+00
etotal13   -2.0947909992E+00
etotal14   -2.0963851177E+00
etotal21   -2.0969713557E+00
etotal22   -2.0975525285E+00
etotal23   -2.0978233733E+00
etotal24   -2.0979980153E+00
etotal31   -2.0983520905E+00
etotal32   -2.0983215368E+00
etotal33   -2.0983305960E+00
etotal34   -2.0984218116E+00

etotal 24 is -2.0979980153E+00 Ha, with an accuracy of 0.0005 Ha .

## 4 Surface energy of aluminum (100): changing the orientation of the unit cell¶

In order to study the Aluminum (100) surface, we will have to set up a supercell representing a slab. This supercell should be chosen as to be compatible with the primitive surface unit cell.
The corresponding directions are [-1 1 0] and [1 1 0]. The direction perpendicular to the surface is [0 0 1]. There is no primitive cell of bulk aluminum based on these vectors, but a doubled cell. We will first compute the total energy associated with this doubled cell. This is not strictly needed, but it is a valuable intermediate step towards the study of the surface.

You might start from tbase4_3.in.
You have to change rprim. Still, try to keep acell at the values of bulk aluminum that were determined previously. But it is not all: the most difficult part in the passage to this doubled cell is the definition of the k-point grid. Of course, one could just take a homogeneous simple cubic grid of k points, but this will not correspond exactly to the k-point grid used in the primitive cell in tbase4_3.in. This would not be a big problem, but you would miss some error cancellation.

The answer to this problem is given in the input file ~abinit/tests/tutorial/Input/tbase4_4.in.

The procedure to do the exact translation of the k-point grid will not be explained here (sorry for this). If you do not see how to do it, just use homogeneous simple cubic grids, with about the same resolution as for the primitive cell case. There is a simple rule to estimate roughly whether two grids for different cells have the same resolution: simply multiply the linear dimensions of the k-point grids, by the number of sublattices, by the number of atoms in the cell. For example, the corresponding product for the usual 10 k-point grid is 4x4x4 x 4 x 1 = 256. In the file tbase4_4.in, one has 4x4x4 x 2 x 2 = 256. The grids of k points should not be too anisotropic for this rough estimation to be valid.

Note also the input variables rprim and chkprim in this input file.

So, you run tbase4_4.in (only a few seconds, the reference file is ~abinit/tests/tutorial/Refs/tbase4_4.out), and you find the following total energy:

           etotal     -4.1962972610E+00

It is not exactly twice the total energy for the primitive cell, mentioned above, but the difference is less than 0.0005 Ha. It is due to the different FFT grids used in the two runs, and affect the exchange-correlation energy. These grids are always homogeneous primitive 3D grids, so that changing the orientation of the lattice will give mutually incompatible lattices. Increasing the size of the FFT grid would improve the agreement.

## 5 Surface energy: a (3 aluminum layer + 1 vacuum layer) slab calculation¶

We will first compute the total energy associated with only three layers of aluminum, separated by only one layer of vacuum. This is kind of a minimal slab:

• one surface layer
• one “bulk” layer
• one surface layer
• one vacuum layer

It is convenient to take the vacuum region as having a multiple of the width of the aluminum layers, but this is not mandatory. The supercell to use is the double of the previous cell (that had two layers of Aluminum atoms along the [0 0 1] direction). Of course, the relaxation of the surface might give an important contribution to the total energy.

You should start from tbase4_4.in.
You have to modify rprim (double the cell along [0 0 1]), the atomic positions, as well as the k point mesh. For the latter, it is supposed that the electrons cannot propagate from one slab to its image in the [0 0 1] direction, so that the k_z component of the special k points can be taken 0: only one layer of k points is needed along the z-direction. You should also allow the relaxation of atomic positions, but not the relaxation of lattice parameters (the lattice parameters along x or y must be considered fixed to the bulk value, while, for the z direction, there is no interest to allow the vacuum region to collapse!

The input file ~abinit/tests/tutorial/Input/tbase4_5.in is an example, while ~abinit/tests/tutorial/Refs/tbase4_5.out is a reference output file. The run might last one minute.

The total energy after the first SCF cycle, when the atomic positions are equal to their starting values, is:

 ETOT  6  -6.2619738807344

Note that the total energy of three aluminum atoms in the bulk, (from section 4.3, etotal24 multiplied by three) is

   -6.293994 Ha

so that the non-relaxed surface energy, per surface unit cell (there are two surfaces in our simulation cell!) is

  0.016010 Ha = 0.436 eV.

The total energy after the Broyden relaxation is:

           etotal     -6.2622251508E+00

so that the relaxed surface energy, per surface unit cell is

0.015885 Ha = 0.432eV.

It seems that the relaxation energy is very small, compared to the surface energy, but we need to do the convergence studies.

## 6 Surface energy: increasing the number of vacuum layers¶

One should now increase the number of vacuum layers: 2 and 3 layers instead of only 1.
It is preferable to define atomic positions in Cartesian coordinates. The same coordinates will work for both 2 and 3 vacuum layers, while this is not the case for reduced coordinates, as the cell size increases.

The input file ~abinit/tests/tutorial/Input/tbase4_6.in is an example input file, while ~abinit/tests/tutorial/Refs/tbase4_6.out is a reference output file. The run is on the order of thirty seconds on a PC 3 GHz.

In the Broyden step 0 of the first dataset, you will notice the WARNING:

 scprqt:  WARNING -
nstep=    6 was not enough SCF cycles to converge;
maximum force difference=  5.493E-05 exceeds toldff=  5.000E-05

The input variable nstep was intentionally set to the rather low value of 6, to warn you about possible convergence difficulties. The SCF convergence might indeed get more and more difficult with cell size. This is because the default preconditioner (see the notice of the input variable dielng) is not very good for the metal+vacuum case.
For the interpretation of the present run, this is not critical, as the convergence criterion was close of being fulfilled, but one should keep this in mind, as you will see …

For the 2 vacuum layer case, one has the non-relaxed total energy:

 ETOT  6  -6.2539524271719

giving the unrelaxed surface energy

  0.0200 Ha = 0.544 eV;

and for the relaxed case:

           etotal1    -6.2547006435E+00

(this one is converged to the required level) giving the relaxed surface energy

  0.0196 Ha = 0.533 eV

Note that the difference between unrelaxed and relaxed case is a bit larger than in the case of one vacuum layer. This is because there was some interaction between slabs of different supercells.

For the 3 vacuum layer case, the self-consistency is slightly more difficult than with 2 vacuum layers: the Broyden step 0 is not sufficiently converged (one might set nstep to a larger value, but the best is to change the preconditioner, as described below)…
However, for the Broyden steps number 2 and beyond, because one takes advantage of the previous wavefunctions, a sufficient convergence is reached. The total energy, in the relaxed case, is:

           etotal2    -6.2559103620E+00

giving the relaxed surface energy 0.0190 Ha = 0.515 eV There is a rather small 0.018 eV difference with the 2 vacuum layer case.

For the next run, we will keep the 2 vacuum layer case, and we know that the accuracy of the coming calculation cannot be better than 0.016 eV. One might investigate the 4 vacuum layer case, but this is not worth, in the present tutorial …

## 7 Surface energy: increasing the number of aluminum layers¶

One should now increase the number of aluminum layers, while keeping 2 vacuum layers. We will consider 4 and 5 aluminum layers. This is rather straightforward to set up, but will also change the preconditioner. One could use an effective dielectric constant of about 3 or 5, with a rather small mixing coefficient, on the order of 0.2. However, there is also another possibility, using an estimation of the dielectric matrix governed by iprcel=45 . For comparison with the previous treatment of SCF, one can recompute the result with 3 aluminum layers.

The input file ~abinit/tests/tutorial/Input/tbase4_7.in is an example, while ~abinit/tests/tutorial/Refs/tbase4_7.out is a reference output file. This run might take about one minute, and is the longer of the four basic lessons. You should start it now.

You can monitor its evolution by editing from time to time the tbase4_7_STATUS file that the code updates regularly. The status file, that refer to the skeleton of the code, is described in the ~abinit/doc/developers/programmer_guide.txt. You might take advantage of the time of the run to explore the files contained in the ~abinit/doc/users directory and the ~abinit/doc/developers directory. The README files provided interesting entry points in the documentation of the code.

Coming back to the file tbase4_7.out …
You will notice that the SCF convergence is rather satisfactory, for all the cases (3, 4 or 5 metal layers).

For the 3 aluminum layer case, one has the non-relaxed total energy:

 ETOT  6  -6.2539524363433

(this quantity is converged, unlike in test 4.6)
giving the unrelaxed surface energy 0.0200 Ha = 0.544 eV ; and for the relaxed case:

           etotal1    -6.2547008127E+00

(by contrast the difference with test 4.6 is less than 1 microHa)
giving the relaxed surface energy 0.0196 Ha = 0.533 eV .

For the 4 aluminum layer case, one has the non-relaxed total energy:

 ETOT  6  -8.3546873357119

giving the unrelaxed surface energy 0.0186Ha = 0.506 eV; and for the relaxed case:

           etotal2    -8.3565593186E+00

giving the relaxed surface energy 0.0183 Ha = 0.498 eV.

For the 5 aluminum layer case, one has the non-relaxed total energy:

 ETOT  6  -10.453642176439

giving the unrelaxed surface energy 0.0183Ha = 0.498 eV; and for the relaxed case:

           etotal3    -1.0454163186E+01

giving the relaxed surface energy 0.0180 Ha = 0.490 eV .

The relative difference in the surface energy of the 4 and 5 layer cases is on the order of 1.5%.

In the framework of this tutorial, we will not pursue this investigation, which is a simple application of the concepts already explored.

Just for your information, and as an additional warning, when the work accomplished until now is completed with 6 and 7 layers without relaxation (see ~abinit/tests/tutorial/Input/tbase4_8.in and ~abinit/tests/tutorial/Refs/tbase4_8.out where 5, 6 and 7 layers are treated), this non-relaxed energy surface energy behaves as follows:

number of aluminum layers surface energy
3 0.544 eV
4 0.506 eV
5 0.498 eV
6 0.449 eV
7 0.463 eV

So, the surface energy convergence is rather difficult to reach.
Our values, with a 4x4x1 grid, a smearing of 0.04 Ha, a kinetic energy cut- off of 6 Ha, the 13al.981214.fhi pseudopotential, still oscillate between 0.45 eV and 0.51 eV. Increasing the k point sampling might decrease slightly the oscillations, but note that this effect is intrinsic to the computation of properties of a metallic surface: the electrons are confined inside the slab potential, with subbands in the direction normal to the surface, and the Fermi energy oscillates with the width of the slab. This effect might be understood based on a comparison with the behaviour of a jellium slab.
An error on the order of 0.016 eV is due to the thin vacuum layer. Other sources of errors might have to be rechecked, seeing the kind of accuracy that is needed.

Experimental data give a surface energy around 0.55 eV (sorry, the reference is to be provided).


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# Knowing the Galois group of the splitting field of a polynomial $f$, how can I show that $f$ is irreducible in the ground field?

So I'm given $f(x) = \sum_{k=0}^{8}\frac{x^k}{k!} \in \mathbb{Q}[x]$. Denote its splitting field by $E$, then I'm also given that ${\rm Gal}(E/\mathbb{Q}) \cong A_8$. The task is to prove that $f(x)$ is irreducible over $\mathbb{Q}$.

So $A_8$ is known to be simple, so by the fundamental theorem there cannot exist intermediate fields $\mathbb{Q} \subset K \subset E$ such that $\mathbb{Q} \subset K$ is normal. So if $f$ is reducible over $\mathbb{Q}$, but not completely, then the splitting field of the remaining irreducible polynomial will also be $E$. Any irreducible polynomial in $\mathbb{Q}[x]$ which splits in $E$ will not split in any subfield of $E$ containing $\mathbb{Q}$.

Assuming that my reasoning so far is correct, I cannot see how to proceed from here. I don't quite see for instance how it can't be the case that one root of $f$ lies in $\mathbb{Q}$ and the rest in $E$. Any help is appreciated.

• Note that if one root was in $\Bbb Q$ and the rest were in $E$, then the action of a Galois automorphism would be determined by its action on the seven roots not in $\Bbb Q$. Thus, the Galois group would be isomorphic to a subgroup of $S_7$. – Rolf Hoyer Jun 8 '16 at 16:39
• @RolfHoyer Oh right! It's only true that the Galois group is isomorphic to a subgroup of $S_r$ if $f$ has $r$ distinct roots in the splitting field, right? Of course, this is the case here since $\mathbb{Q}$ has characteristic 0. – Auclair Jun 8 '16 at 16:42

You can appeal to the fact that $f$ is irreducible iff the Galois group acts transitively on the set of roots. Here, we expect that $\text{Gal}(E/\mathbb{Q}) \cong A_8$ under the action of the Galois group on the roots, but let's ensure that is true:
Consider the action of the Galois group on the $n$ roots of $f$ in $\mathbb{C}$. This induces a homomorphism $f:A_8 \to S_n$. Since $A_8$ is simple, this must be injective, and so $n \geq 8$. Since $n\leq 8$ anyway, $n=8$. So $[S_8:f(A_8)] = 2$, so $f(A_8) \vartriangleleft S_8$, whence $f(A_8) = A_8$. In particular, the Galois group acts transitively on the set of roots of $f$.
So, $f$ is irreducible.

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## Displaying Chemical Equations

Discussions on general chemistry and chemical engineering, organic chemistry, analytical chemistry, etc.

### Displaying Chemical Equations

Here is a neat way to display chemical equations using the formula function.

Code: Select all
$$\text 2H_2O \longrightarrow[50]\limits^{elect.} 2H_2 + O_2$$

renders as:

$\text 2H_2O \longrightarrow[50]\limits^{elect.} 2H_2 + O_2$

You can also add \text at the beginning so it would read out the spaces, Hence:

Code: Select all
$$\text 2H_2O \longrightarrow[50]\limits^{elect.} 2H_2 + O_2$$

$\fs2 \text 2H_2O \longrightarrow[50]\limits^{elect.} 2H_2 + O_2$

Some more examples:

Code: Select all
1: $$A + B \rightleftharpoons C + B$$2: $$\text A + B \rightleftharpoons C + B$$3: $$\text A + B \longrightarrow^{heat} C + D$$4: $$\text A + B \longrightarrow[50]^{X + Y} C + D$$5: $$\text A + B \longrightarrow[100]^{X + Y} C + D$$6: $$\text 2X_2Y_3 + Z_3^+ \longrightarrow W_3^- + 4U^{2+}$$

1: $A + B \rightleftharpoons C + B$

2: $\text A + B \rightleftharpoons C + B$

3: $\text A + B \longrightarrow^{heat} C + D$

4: $\text A + B \longrightarrow[50]^{X + Y} C + D$

5: $\text A + B \longrightarrow[100]^{X + Y} C + D$

6: $\text 2X_2Y_3 + Z_3^+ \longrightarrow W_3^- + 4U^{2+}$

If you dont include "\text" at the beginning, the text comes out italicized.

Full manual for the script can be found here.


text:
# Natural Numbers under Multiplication form Subsemigroup of Integers

## Theorem

Let $\struct {\N, \times}$ denote the set of natural numbers under multiplication.

Let $\struct {\Z, \times}$ denote the set of integers under multiplication.

Then $\struct {\N, \times}$ is a subsemigroup of $\struct {\Z, \times}$.

## Proof

We have from Natural Numbers under Multiplication form Semigroup that $\struct {\N, \times}$ forms a semigroup.

We have from Integers under Multiplication form Semigroup that $\struct {\Z, \times}$ forms a semigroup.

From Natural Numbers are Non-Negative Integers, we have that $\N \subseteq \Z$.

From the definition of integer multiplication it follows that $\times: \Z \to \Z$ is an extension of $\times: \N \to \N$.

Hence the result.

$\blacksquare$


text:
• ### The VLA-COSMOS 3 GHz Large Project: The cosmic star formation history since z~5(1703.09724)

March 30, 2017 astro-ph.GA
We make use of the deep Karl G. Jansky Very Large Array (VLA) COSMOS radio observations at 3 GHz to infer radio luminosity functions of star-forming galaxies up to redshifts of z~5 based on approximately 6000 detections with reliable optical counterparts. This is currently the largest radio-selected sample available out to z~5 across an area of 2 square degrees with a sensitivity of rms=2.3 ujy/beam. By fixing the faint and bright end shape of the radio luminosity function to the local values, we find a strong redshift trend that can be fitted with a pure luminosity evolution L~(1+z)^{(3.16 +- 0.2)-(0.32 +- 0.07) z}. We estimate star formation rates (SFRs) from our radio luminosities using an infrared (IR)-radio correlation that is redshift dependent. By integrating the parametric fits of the evolved luminosity function we calculate the cosmic SFR density (SFRD) history since z~5. Our data suggest that the SFRD history peaks between 2<z<3 and that the ultraluminous infrared galaxies (ULIRGs; 100 Msol/yr<SFR<1000 Msol/yr) contribute up to ~25% to the total SFRD in the same redshift range. Hyperluminous infrared galaxies (HyLIRGs; SFR>1000 Msol/yr) contribute an additional <2% in the entire observed redshift range. We find evidence of a potential underestimation of SFRD based on ultraviolet (UV) rest-frame observations of Lyman break galaxies (LBGs) at high redshifts (z>4) on the order of 15-20%, owing to appreciable star formation in highly dust-obscured galaxies, which might remain undetected in such UV observations.
• ### The VLA-COSMOS 3 GHz Large Project: Continuum data and source catalog release(1703.09713)

March 28, 2017 astro-ph.GA
We present the VLA-COSMOS 3 GHz Large Project based on 384 hours of observations with the Karl G. Jansky Very Large Array (VLA) at 3 GHz (10 cm) toward the two square degree Cosmic Evolution Survey (COSMOS) field. The final mosaic reaches a median rms of 2.3 uJy/beam over the two square degrees at an angular resolution of 0.75". To fully account for the spectral shape and resolution variations across the broad (2 GHz) band, we image all data with a multiscale, multifrequency synthesis algorithm. We present a catalog of 10,830 radio sources down to 5 sigma, out of which 67 are combined from multiple components. Comparing the positions of our 3 GHz sources with those from the Very Long Baseline Array (VLBA)-COSMOS survey, we estimate that the astrometry is accurate to 0.01" at the bright end (signal-to-noise ratio, S/N_3GHz > 20). Survival analysis on our data combined with the VLA-COSMOS 1.4~GHz Joint Project catalog yields an expected median radio spectral index of alpha=-0.7. We compute completeness corrections via Monte Carlo simulations to derive the corrected 3 GHz source counts. Our counts are in agreement with previously derived 3 GHz counts based on single-pointing (0.087 square degrees) VLA data. In summary, the VLA-COSMOS 3 GHz Large Project simultaneously provides the largest and deepest radio continuum survey at high (0.75") angular resolution to date, bridging the gap between last-generation and next-generation surveys.
• ### The composite nature of Dust-Obscured Galaxies (DOGs) at z~2-3 in the COSMOS field: I. A Far-Infrared View(1506.05475)

June 17, 2015 astro-ph.GA
Dust-Obscured galaxies (DOGs) are bright 24 um-selected sources with extreme obscuration at optical wavelengths. They are typically characterized by a rising power-law continuum of hot dust (T_D ~ 200-1000K) in the near-IR indicating that their mid-IR luminosity is dominated by an an active galactic nucleus (AGN). DOGs with a fainter 24 um flux display a stellar bump in the near-IR and their mid-IR luminosity appears to be mainly powered by dusty star formation. Alternatively, it may be that the mid-IR emission arising from AGN activity is dominant but the torus is sufficiently opaque to make the near-IR emission from the AGN negligible with respect to the emission from the host component. In an effort to characterize the astrophysical nature of the processes responsible for the IR emission in DOGs, this paper exploits Herschel data (PACS + SPIRE) on a sample of 95 DOGs within the COSMOS field. We derive a wealth of far-IR properties (e.g., total IR luminosities; mid-to-far IR colors; dust temperatures and masses) based on SED fitting. Of particular interest are the 24 um-bright DOGs (F_24um > 1mJy). They present bluer far-IR/mid-IR colors than the rest of the sample, unveiling the potential presence of an AGN. The AGN contribution to the total 8-1000 um flux increases as a function of the rest-frame 8 um-luminosity irrespective of the redshift. This confirms that faint DOGs (L_8 um< 10^12 L_sun) are dominated by star-formation while brighter DOGs show a larger contribution from an AGN.
• ### A proto-cluster at z=2.45(1411.0649)

Nov. 6, 2014 astro-ph.CO
We present the spectroscopic confirmation of a $z=2.45$ proto-cluster. Its member galaxies lie within a radius of 1.4Mpc (physical) on the sky and within $\Delta v \pm 700$km/s along the line of sight. We estimate an overdensity of 10, suggesting that the structure has made the turn-around but is not assembled yet. Comparison to the Millennium simulation suggests that analogous structures evolve into $10^{14}-10^{15}$M$_{\odot}$/h type dark matter haloes by $z=0$ qualifying the notion of "proto-cluster". The search for the complete census of mock progenitor galaxies at $z\sim2.5$ of these massive $z=0$ mock clusters reveals that they are widely spread over areas with a diameter of 3-20Mpc. This suggests that the optical selection of such proto-clusters can result in a rich diversity regarding their $z=0$ descendants. We also searched for signs of environmental differentiation in this proto-cluster. Whilst we see a weak trend for more massive and more quiescent galaxies in the proto-cluster, this is not statistically significant.
• ### Sub-millimeter galaxies as progenitors of compact quiescent galaxies(1401.1510)

Jan. 7, 2014 astro-ph.CO, astro-ph.GA
Three billion years after the big bang (at redshift z=2), half of the most massive galaxies were already old, quiescent systems with little to no residual star formation and extremely compact with stellar mass densities at least an order of magnitude larger than in low redshift ellipticals, their descendants. Little is known about how they formed, but their evolved, dense stellar populations suggest formation within intense, compact starbursts 1-2 Gyr earlier (at 3<z<6). Simulations show that gas-rich major mergers can give rise to such starbursts which produce dense remnants. Sub-millimeter selected galaxies (SMGs) are prime examples of intense, gas-rich, starbursts. With a new, representative spectroscopic sample of compact quiescent galaxies at z=2 and a statistically well-understood sample of SMGs, we show that z=3-6 SMGs are consistent with being the progenitors of z=2 quiescent galaxies, matching their formation redshifts and their distributions of sizes, stellar masses and internal velocities. Assuming an evolutionary connection, their space densities also match if the mean duty cycle of SMG starbursts is 42 (+40/-29) Myr (consistent with independent estimates), which indicates that the bulk of stars in these massive galaxies were formed in a major, early surge of star-formation. These results suggests a coherent picture of the formation history of the most massive galaxies in the universe, from their initial burst of violent star-formation through their appearance as high stellar-density galaxy cores and to their ultimate fate as giant ellipticals.
• ### Discovery of bright z ~ 7 galaxies in the UltraVISTA survey(1205.4270)

Sept. 4, 2012 astro-ph.CO
We have exploited the new, deep, near-infrared UltraVISTA imaging of the COSMOS field, in tandem with deep optical and mid-infrared imaging, to conduct a new search for luminous galaxies at redshifts z ~ 7. The unique multi-wavelength dataset provided by VISTA, CFHT, Subaru, HST and Spitzer over a common area of 1 deg^2 has allowed us to select galaxy candidates at z > 6.5 by searching first for Y+J-detected (< 25 AB mag) objects which are undetected in the CFHT+HST optical data. This sample was then refined using a photometric redshift fitting code, enabling the rejection of lower-redshift galaxy contaminants and cool galactic M,L,T dwarf stars.The final result of this process is a small sample of (at most) ten credible galaxy candidates at z > 6.5 which we present in this paper. The first four of these appear to be robust galaxies at z > 6.5, and fitting to their stacked SED yields z = 6.98+-0.05 with a stellar mass M* = 5x10^9 Msun, and rest-frame UV spectral slope beta = -2.0+-0.2. The next three are also good candidates for z > 6.5 galaxies, but the possibility that they are low-redshift galaxies or dwarf stars cannot be excluded. Our final subset of three additional candidates is afflicted not only by potential dwarf-star contamination, but also contains objects likely to lie at redshifts just below z = 6.5. We show that the three even-brighter z > 7 galaxy candidates reported in the COSMOS field by Capak et al. (2011) in fact all lie at z ~ 1.5-3.5. Consequently the new z ~ 7 galaxies reported here are the first credible z ~ 7 Lyman-break galaxies discovered in the COSMOS field and, as the most UV-luminous discovered to date at these redshifts, are prime targets for deep follow-up spectroscopy. We explore their physical properties, and briefly consider the implications of their inferred number density for the form of the galaxy luminosity function at z = 7.
• Euclid is a space-based survey mission from the European Space Agency designed to understand the origin of the Universe's accelerating expansion. It will use cosmological probes to investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the universe and on the cosmic history of structure formation. The mission is optimised for two independent primary cosmological probes: Weak gravitational Lensing (WL) and Baryonic Acoustic Oscillations (BAO). The Euclid payload consists of a 1.2 m Korsch telescope designed to provide a large field of view. It carries two instruments with a common field-of-view of ~0.54 deg2: the visual imager (VIS) and the near infrared instrument (NISP) which contains a slitless spectrometer and a three bands photometer. The Euclid wide survey will cover 15,000 deg2 of the extragalactic sky and is complemented by two 20 deg2 deep fields. For WL, Euclid measures the shapes of 30-40 resolved galaxies per arcmin2 in one broad visible R+I+Z band (550-920 nm). The photometric redshifts for these galaxies reach a precision of dz/(1+z) < 0.05. They are derived from three additional Euclid NIR bands (Y, J, H in the range 0.92-2.0 micron), complemented by ground based photometry in visible bands derived from public data or through engaged collaborations. The BAO are determined from a spectroscopic survey with a redshift accuracy dz/(1+z) =0.001. The slitless spectrometer, with spectral resolution ~250, predominantly detects Ha emission line galaxies. Euclid is a Medium Class mission of the ESA Cosmic Vision 2015-2025 programme, with a foreseen launch date in 2019. This report (also known as the Euclid Red Book) describes the outcome of the Phase A study.
• ### Dissecting Photometric redshift for Active Galactic Nuclei using XMM- and Chandra-COSMOS samples(1108.6061)

Aug. 30, 2011 astro-ph.CO
With this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the COSMOS field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by AGN-dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy sigma_(Delta z/(1+z_spec)) \sim0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 sq. deg.of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by Delta z>0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry H_AB=24 mag. We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together with the number and the depth of the available bands influence the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGN, such as eROSITA at X-ray energies and ASKAP/EMU in the radio band.
• ### The redshift and nature of AzTEC/COSMOS 1: A starburst galaxy at z=4.6(1102.4329)

Aug. 15, 2011 astro-ph.CO
Based on broad/narrow-band photometry and Keck DEIMOS spectroscopy we report a redshift of z=4.64-0.08+0.06 for AzTEC/COSMOS 1, the brightest sub-mm galaxy in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 micron), CSO/SHARC II (350 micron), CARMA and PdBI (3 mm). We do not detect CO(5-4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3sigma upper limits on the gas mass to <~8x10^9 M_Sol and <~5x10^10 M_Sol, respectively (assuming similar conditions as observed in z~2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (<~50 Myr), massive (M*~10^11 M_Sol), but compact (<~2 kpc) galaxy forming stars at a rate of ~1300 M_Sol/yr. Our results imply that AzTEC 1 is forming stars in a 'gravitationally bound' regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.
• ### The lesser role of starbursts for star formation at z=2(1108.0933)

Aug. 3, 2011 astro-ph.CO
Two main modes of star formation are know to control the growth of galaxies: a relatively steady one in disk-like galaxies, defining a tight star formation rate (SFR)-stellar mass sequence, and a starburst mode in outliers to such a sequence which is generally interpreted as driven by merging. Such starburst galaxies are rare but have much higher SFRs, and it is of interest to establish the relative importance of these two modes. PACS/Herschel observations over the whole COSMOS and GOODS-South fields, in conjunction with previous optical/near-IR data, have allowed us to accurately quantify for the first time the relative contribution of the two modes to the global SFR density in the redshift interval 1.5<z<2.5, i.e., at the cosmic peak of the star formation activity. The logarithmic distributions of galaxy SFRs at fixed stellar mass are well described by Gaussians, with starburst galaxies representing only a relatively minor deviation that becomes apparent for SFRs more than 4 times higher than on the main sequence. Such starburst galaxies represent only 2% of mass-selected star forming galaxies and account for only 10% of the cosmic SFR density at z~2. Only when limited to SFR>1000M(sun)/yr, off-sequence sources significantly contribute to the SFR density (46+/-20%). We conclude that merger-driven starbursts play a relatively minor role for the formation of stars in galaxies, whereas they may represent a critical phase towards the quenching of star formation and morphological transformation in galaxies.
• ### The evolution of quiescent galaxies at high redshift (z > 1.4)(1106.3194)

June 17, 2011 astro-ph.CO
We have studied the evolution of high redshift quiescent galaxies over an effective area of ~1.7 deg^2 in the COSMOS field. Galaxies have been divided according to their star-formation activity and the evolution of the different populations has been investigated in detail. We have studied an IRAC (mag_3.6 < 22.0) selected sample of ~18000 galaxies at z > 1.4 with multi-wavelength coverage. We have derived accurate photometric redshifts (sigma=0.06) and other important physical parameters through a SED-fitting procedure. We have divided our sample into actively star-forming, intermediate and quiescent galaxies depending on their specific star formation rate. We have computed the galaxy stellar mass function of the total sample and the different populations at z=1.4-3.0. We have studied the properties of high redshift quiescent galaxies finding that they are old (1-4 Gyr), massive (log(M/M_sun)~10.65), weakly star forming stellar populations with low dust extinction (E(B-V) < 0.15) and small e-folding time scales (tau ~ 0.1-0.3 Gyr). We observe a significant evolution of the quiescent stellar mass function from 2.5 < z < 3.0 to 1.4 < z < 1.6, increasing by ~ 1 dex in this redshift interval. We find that z ~ 1.5 is an epoch of transition of the GSMF. The fraction of star-forming galaxies decreases from 60% to 20% from z ~ 2.5-3.0 to z ~ 1.4-1.6 for log(M/M_sun) > 11, while the quiescent population increases from 10% to 50% at the same redshift and mass intervals. We compare the fraction of quiescent galaxies derived with that predicted by theoretical models and find that the Kitzbichler & White (2007) model is the one that better reproduces the data. Finally, we calculate the stellar mass density of the star-forming and quiescent populations finding that there is already a significant number of quiescent galaxies at z > 2.5 (rho~6.0 MsunMpc^-3).
• ### Spectroscopy of luminous z>7 galaxy candidates and sources of contamination in z>7 galaxy searches(0910.0444)

Jan. 21, 2011 astro-ph.CO
We present three bright z+ dropout candidates selected from deep Near-Infrared (NIR) imaging of the COSMOS 2 square degree field. All three objects match the 0.8-8um colors of other published z>7 candidates but are three magnitudes brighter, facilitating further study. Deep spectroscopy of two of the candidates covering 0.64-1.02um with Keck-DEIMOS and all three covering 0.94-1.10um and 1.52-1.80um with Keck-NIRSPEC detects weak spectral features tentatively identified as Ly-alpha at z=6.95 and z=7.69 in two of the objects. The third object is placed at z~1.6 based on a 24um and weak optical detection. A comparison with the spectral energy distributions of known z<7 galaxies, including objects with strong spectral lines, large extinction, and large systematic uncertainties in the photometry yields no objects with similar colors. However, the lambda>1um properties of all three objects can be matched to optically detected sources with photometric redshifts at z~1.8, so the non-detection in the i+ and z+ bands are the primary factors which favors a z>7 solution. If any of these objects are at z~7 the bright end of the luminosity function is significantly higher at z>7 than suggested by previous studies, but consistent within the statistical uncertainty and the dark matter halo distribution. If these objects are at low redshift, the Lyman-Break selection must be contaminated by a previously unknown population of low redshift objects with very strong breaks in their broad band spectral energy distributions and blue NIR colors. The implications of this result on luminosity function evolution at high redshift is discussed. We show that the primary limitation of z>7 galaxy searches with broad filters is the depth of the available optical data.
• ### The optical spectra of Spitzer 24 micron galaxies in the COSMOS field: II. Faint infrared sources in the zCOSMOS-bright 10k catalogue(0910.5824)

Oct. 30, 2009 astro-ph.CO
We have used the zCOSMOS-bright 10k sample to identify 3244 Spitzer/MIPS 24-micron-selected galaxies with 0.06< S(24um)< 0.50 mJy and I(AB)<22.5, over 1.5 deg^2 of the COSMOS field, and studied different spectral properties, depending on redshift. At 0.2<z<0.3, we found that different reddening laws of common use in the literature explain the dust extinction properties of around 80% of our infrared (IR) sources, within the error bars. For up to 16% of objects, instead, the Halpha/Hbeta ratios are too high for their IR/UV attenuations, which is probably a consequence of inhomogenous dust distributions. In only a few of our galaxies at 0.2<z<0.3 the IR emission could be mainly produced by dust heated by old rather than young stars. Besides, the line ratios of ~22% of our galaxies suggest that they might be star-formation/nuclear-activity composite systems. At 0.5<z<0.7, we estimated galaxy metallicities for 301 galaxies: at least 12% of them are securely below the upper-branch mass-metallicity trend, which is consistent with the local relation. Finally, we performed a combined analysis of the Hdelta equivalent-width versus Dn(4000) diagram for 1722 faint and bright 24um galaxies at 0.6<z<1.0, spanning two decades in mid-IR luminosity. We found that, while secondary bursts of star formation are necessary to explain the position of the most luminous IR galaxies in that diagram, quiescent, exponentially-declining star formation histories can well reproduce the spectral properties of ~40% of the less luminous sources. Our results suggest a transition in the possible modes of star formation at total IR luminosities L(TIR)=(3 +/-2)x10^11 Lsun.
• ### The SINS survey: SINFONI Integral Field Spectroscopy of z ~ 2 Star-forming Galaxies(0903.1872)

Oct. 23, 2009 astro-ph.CO, astro-ph.GA
We present the SINS survey with SINFONI of high redshift galaxies. With 80 objects observed and 63 detected, SINS is the largest survey of spatially resolved gas kinematics, morphologies, and physical properties of star-forming galaxies at z~1-3. We describe the selection of the targets, the observations, and the data reduction. We then focus on the "SINS Halpha sample" of 62 rest-UV/optically-selected sources at 1.3<z<2.6 for which we targeted primarily the Halpha and [NII] emission lines. Only 30% of this sample had previous near-IR spectroscopic observations. As a whole, the SINS Halpha sample covers a reasonable representation of massive log(M*/Msun)>~10 star-forming galaxies at z~1.5-2.5, with some bias towards bluer systems compared to pure K-selected samples due to the requirement of secure optical redshift. The sample spans two orders of magnitude in stellar mass and in absolute and specific star formation rates, with median values of approximately log(M*/Msun) = 10.5, 70 Msun/yr, and 3/Gyr. The ionized gas distribution and kinematics are spatially resolved on scales ranging from 1.5 kpc for adaptive optics assisted observations to typically 4-5 kpc for seeing-limited data. The Halpha morphologies tend to be irregular and/or clumpy. About one-third are rotation-dominated yet turbulent disks, another third comprises compact and velocity dispersion-dominated objects, and the remaining galaxies are clear interacting/merging systems; the fraction of rotation-dominated systems increases among the more massive part of the sample. The Halpha luminosities and equivalent widths suggest on average roughly twice higher dust attenuation towards the HII regions relative to the bulk of the stars, and comparable current and past-averaged star formation rates. [Abridged]
• ### Designing Future Dark Energy Space Mission: I. Building Realistic Galaxy Spectro-Photometric Catalogs and their first applications(0902.0625)

July 13, 2009 astro-ph.CO
Future dark energy space missions such as JDEM and EUCLID are being designed to survey the galaxy population to trace the geometry of the universe and the growth of structure, which both depend on the cosmological model. To reach the goal of high precision cosmology they need to evaluate the capabilities of different instrument designs based on realistic mock catalog. The aim of this paper is to construct realistic and flexible mock catalogs based on our knowledge of galaxy population from current deep surveys. We explore two categories of mock catalog : (i) based on luminosity functions fit of observations (GOODS, UDF,COSMOS,VVDS) using the Le Phare software (ii) based on the observed COSMOS galaxy distribution which benefits from all the properties of the data-rich COSMOS survey. For these two catalogs, we have produced simulated number counts in several bands, color diagrams and redshift distribution for validation against real observational data. We also derive some basic requirements to help designing future Dark Energy mission in terms of number of galaxies available for the weak-lensing analysis as a function of the PSF size and depth of the survey. We also compute the spectroscopic success rate for future spectroscopic redshift surveys (i) aiming at measuring BAO in the case of the wide field spectroscopic redshift survey, and (ii) for the photometric redshift calibration survey which is required to achieve weak lensing tomography with great accuracy. They will be publicly accessible at http://lamwws.oamp.fr/cosmowiki/RealisticSpectroPhotCat, or by request to the first author of this paper.
• ### Environmental Effects on the Star Formation Activity in Galaxies at z=1.2 in the COSMOS Field(0905.3982)

May 27, 2009 astro-ph.CO
We investigate the relation between the star-formation activity in galaxies and environment at z=1.2 in the COSMOS field, using the fraction of [OII] emitters and the local galaxy density. The fraction of [OII] emitters appears to be almost constant over the surface density of galaxies between 0.2 and 10 Mpc^-2. This trend is different from that seen in the local universe where the star-formation activity is weaker in higher density regions. To understand this difference between z~1 and z~0, we study the fraction of non-isolated galaxies as a function of local galaxy density. We find that the fraction of non-isolated galaxies increases with increasing density. Our results suggest that the star formation in galaxies at z~1 is triggered by galaxy interaction and/or mergers.
• ### The spatial clustering of X-ray selected AGN in the XMM-COSMOS field(0810.4769)

Dec. 2, 2008 astro-ph
We study the spatial clustering of 538 X-ray selected AGN in the 2 deg^2 XMM-COSMOS field that are spectroscopically identified to I_{AB}<23 and span the redshift range z=0.2-3.0. The median redshift and luminosity of the sample are z = 0.98 and L_{0.5-10}=6.3 x 10^{43} erg/s, respectively. A strong clustering signal is detected at ~18sigma level, which is the most significant measurement obtained to date for clustering of X-ray selected AGN. By fitting the projected correlation function w(r_p) with a power law on scales of r_p=0.3-40 Mpc/h, we derive a best fit comoving correlation length of r_0 = 8.6 +- 0.5 Mpc/h and slope of gamma=1.88 +- 0.07 (Poissonian errors; bootstrap errors are about a factor of 2 larger). An excess signal is observed in the range r_p~5-15 Mpc/h, which is due to a large scale structure at z ~ 0.36 containing about 40 AGN. When removing the z ~ 0.36 structure, or computing w(r_p) in a narrower range around the peak of the redshift distribution (e.g. z=0.4-1.6), the correlation length decreases to r_0 ~ 5-6 Mpc/h, which is consistent with that observed for bright optical QSOs at the same redshift. We investigate the clustering properties of obscured and unobscured AGN separately. Within the statistical uncertainties, we do not find evidence that AGN with broad optical lines (BLAGN) cluster differently from AGN without broad optical lines (non-BLAGN). The correlation length measured for XMM-COSMOS AGN at z~1 is similar to that of massive galaxies (stellar mass M_*> 3 x 10^{10} M_sun) at the same redshift. This suggests that AGN at z~1 are preferentially hosted by massive galaxies, as observed both in the local and in the distant (z~2) Universe. (shortened)
• ### The close environment of 24 micron galaxies at 0.6<z<1.0 in the COSMOS field(0808.3407)

Sept. 29, 2008 astro-ph
We investigate the close environment of 203 Spitzer 24 micron-selected sources at 0.6<z<1.0 using zCOSMOS-bright redshifts and spectra of I<22.5 AB mag galaxies, over 1.5 sq. deg. of the COSMOS field. We quantify the degree of passivity of the LIRG and ULIRG environments by analysing the fraction of close neighbours with Dn(4000)>1.4. We find that LIRGs at 0.6<z<0.8 live in more passive environments than those of other optical galaxies that have the same stellar mass distribution. Instead, ULIRGs inhabit more active regions (e.g. LIRGs and ULIRGs at 0.6<z<0.8 have, respectively, (42.0 +/- 4.9)% and (24.5 +/- 5.9)% of neighbours with Dn (4000)>1.4 within 1 Mpc and +/- 500 km/s). The contrast between the activities of the close environments of LIRGs and ULIRGs appears especially enhanced in the COSMOS field density peak at z~0.67, because LIRGs on this peak have a larger fraction of passive neighbours, while ULIRGs have as active close environments as those outside the large-scale structure. The differential environmental activity is related to the differences in the distributions of stellar mass ratios between LIRGs/ULIRGs and their close neighbours, as well as in the general local density fields. At 0.8<z<1.0, instead, we find no differences in the environment densities of ULIRGs and other similarly massive galaxies, in spite of the differential activities. We discuss a possible scenario to explain these findings.
• ### Photometric redshift and classification for the XMM-COSMOS sources(0809.2098)

Sept. 11, 2008 astro-ph
We present photometric redshifts and spectral energy distribution (SED) classifications for a sample of 1542 optically identified sources detected with XMM in the COSMOS field. Our template fitting classifies 46 sources as stars and 464 as non-active galaxies, while the remaining 1032 require templates with an AGN contribution. High accuracy in the derived photometric redshifts was accomplished as the result of 1) photometry in up to 30 bands with high significance detections, 2) a new set of SED templates including 18 hybrids covering the far-UV to mid-infrared, which have been constructed by the combination of AGN and non-active galaxies templates, and 3) multi-epoch observations that have been used to correct for variability (most important for type 1 AGN). The reliability of the photometric redshifts is evaluated using the sub-sample of 442 sources with measured spectroscopic redshifts. We achieved an accuracy of $\sigma_{\Delta z/(1+z_{spec})} = 0.014$ for i$_{AB}^*<$22.5 ($\sigma_{\Delta z/(1+z_{spec})} \sim0.015$ for i$_{AB}^*<$24.5). The high accuracies were accomplished for both type 2 (where the SED is often dominated by the host galaxy) and type 1 AGN and QSOs out to $z=4.5$. The number of outliers is a large improvement over previous photometric redshift estimates for X-ray selected sources (4.0% and 4.8% outliers for i$_{AB}^*<$22.5 and i$_{AB}^*<$24.5, respectively). We show that the intermediate band photometry is vital to achieving accurate photometric redshifts for AGN, whereas the broad SED coverage provided by mid infrared (Spitzer/IRAC) bands is important to reduce the number of outliers for normal galaxies.
• ### Spectroscopic Confirmation Of An Extreme Starburst At Redshift 4.547(0806.0657)

June 3, 2008 astro-ph
We report the spectroscopic confirmation of a sub-mm galaxy (SMG) at z=4.547 with an estimated L_IR=0.5-2.0x10^13 L_sun. The spectra, mid-IR, and X-ray properties indicate the bolometric luminosity is dominated by star formation at a rate of >1000M_sun per yr. Multiple, spatially separated components are visible in the Ly-Alpha line with an observed velocity difference of up to 380 km/sec and the object morphology indicates a merger. The best fit spectral energy distribution and spectral line indicators suggest the object is 2-8 Myr old and contains >10^10 M_sun of stellar mass. This object is a likely progenitor for the massive early type systems seen at z~2.
• ### Photometric Redshifts of Galaxies in COSMOS(astro-ph/0612344)

Dec. 13, 2006 astro-ph
We measure photometric redshifts and spectral types for galaxies in the COSMOS survey. We use template fitting technique combined with luminosity function priors and with the option to simultaneously estimate dust extinction (i.e. E(B-V)) for each galaxy.Our estimated redshifts are accurate to i<25 and z~1.2. Using simulations with sampling and noise characteristics similar to those in COSMOS, the accuracy and reliability is estimated for the photometric redshifts as a function of the magnitude limits of the sample, S/N ratios and the number of bands used. From the simulations we find that the ratio of derived 95% confidence interval in the redshift probability distribution to the estimated photometric redshift (D95) can be used to identify and exclude the catastrophic failures in the photometric redshift estimates. We compare the derived redshifts with high-reliability spectroscopic redshifts for a sample of 868 normal galaxies with z < 1.2 from zCOSMOS. Considering different scenarios, depending on using prior, no prior and/or extinction, we compare the photometric and spectroscopic redshifts for this sample. This corresponds to an rms scatter of 0.031, with a small number of outliers (<2.5%). We also find good agreement (rms=0.10) between photometric and spectroscopic redshifts for Type II AGNs. We compare results from our photometric redshift procedure with three other independent codes and find them in excellent agreement. We show preliminary results, based on photometric redshifts for the entire COSMOS sample (to i < 25 mag.).
• ### The Zurich Extragalactic Bayesian Redshift Analyzer (ZEBRA) and its first application: COSMOS(astro-ph/0609044)

Sept. 2, 2006 astro-ph
We present ZEBRA, the Zurich Extragalactic Bayesian Redshift Analyzer. The current version of ZEBRA combines and extends several of the classical approaches to produce accurate photometric redshifts down to faint magnitudes. In particular, ZEBRA uses the template-fitting approach to produce Maximum Likelihood and Bayesian redshift estimates based on: (1.) An automatic iterative technique to correct the original set of galaxy templates to best represent the SEDs of real galaxies at different redshifts; (2.) A training set of spectroscopic redshifts for a small fraction of the photometric sample; and (3.) An iterative technique for Bayesian redshift estimates, which extracts the full two-dimensional redshift and template probability function for each galaxy. We demonstrate the performance of ZEBRA by applying it to a sample of 866 I_AB <= 22.5 COSMOS galaxies with available u*, B, V, g', r', i', z' and K_s photometry and zCOSMOS spectroscopic redshifts in the range 0 < z < 1.3. Adopting a 5-sigma-clipping that excludes less than 10 galaxies, both the Maximum Likelihood and Bayesian estimates for this sample have an accuracy dz/1+z better than 0.03. Similar accuracies are recovered using mock galaxies.
• ### Mid-Infrared Identifications of SCUBA Galaxies in the CUDSS 14-Hour Field with the Spitzer Space Telescope(astro-ph/0603198)

April 21, 2006 astro-ph
We identify 17 possible 8.0 micron-selected counterparts to the submillimeter galaxies in the CUDSS 14-hour field, derived from deep imaging carried out with the IRAC and MIPS instruments aboard the Spitzer Space Telescope. Ten of the 17 counterparts are not the same as those previously identified at shorter wavelengths. We argue that 8.0 micron selection offers a better means for identifying counterparts to submillimeter galaxies than near-infrared or optical selection. Based on the panchromatic SEDs, most counterparts appear to be powered by ongoing star formation. Power-law fits to the SEDs suggest that five objects in the 8.0 micron-selected counterpart sample harbor dominant AGNs; a sixth object is identified as a possible AGN. The 3.6 to 8.0 micron colors of the infrared-selected counterparts are significantly redder than the general IRAC galaxy population in the CUDSS 14-hour field.
• ### An investigation of the submillimeter background radiation using SCUBA and Spitzer(astro-ph/0512357)

Dec. 14, 2005 astro-ph
We investigate the redshift dependence of the contribution to the extragalactic far-infrared/sub-millimeter background from galaxies detected by the Spitzer Space Telescope at 8um and 24um. Using seven-band optical to mid-infrared photometry, we estimate photometric redshifts for the Spitzer sources which appear to be mostly L* galaxies at a median redshift of z=1.0. These sources, extracted from deep 8um and 24um mosaics of the CUDSS 14-hour field with 5sigma limits of 5.8uJy and 70uJy respectively, exhibit significant 850um and 450um emission as observed by SCUBA. At 850um, after removing >=4sigma sources and those securely identified in our previous cross-matching paper, we measure stacked flux at the significance level of 4.4sigma and 2.9sigma from the full 8um and 24um galaxy catalogue respectively. At 450um, flux is detected from all 8um galaxies at the level of 3.5sigma, while there is no significant emission from the 24um galaxies. We find that the 850um flux is emitted almost exclusively at z>~1.3 from the Spitzer sources with 0.44mJy (4.7sigma) per 8um source and 0.51mJy (2.8sigma) per 24um source. This corresponds to a contribution of (16+/-3)% toward the 850um extra-galactic background from the 8um sources and (5.0+/-1.8)% from the 24um sources. At 450um, only the 8um sources within the redshift interval 1<z<2 exhibit significant emission with an average flux per source of 3.35mJy (3.0sigma). This is a contribution of (37+/-12)% to the 450um background.
• ### The XMM-LSS survey. Survey design and first results(astro-ph/0305191)

Nov. 1, 2004 astro-ph
We have designed a medium deep large area X-ray survey with XMM - the XMM Large Scale Structure survey, XMM-LSS - with the scope of extending the cosmological tests attempted using ROSAT cluster samples to two redshift bins between 0<z<1 while maintaining the precision of earlier studies. Two main goals have constrained the survey design: the evolutionary study of the cluster-cluster correlation function and of the cluster number density. The results are promising and, so far, in accordance with our predictions as to the survey sensitivity and cluster number density. The feasibility of the programme is demonstrated and further X-ray coverage is awaited in order to proceed with a truly significant statistical analysis. (Abridged)