281 research outputs found

    Luminosity Functions beyond the spectroscopic limit. I. Method and near-infrared LFs in the HDF-N and HDF-S

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    We have developed a Monte Carlo method to compute the luminosity function of galaxies, based on photometric redshifts, which takes into account the non-gaussianity of the probability functions, and the presence of degenerate solutions in redshift. In this paper we describe the method and the mock tests performed to check its reliability. The NIR luminosity functions and the redshift distributions are determined for near infrared subsamples on the HDF-N and HDF-S. The results on the evolution of the NIR LF, the stellar mass function, and the luminosity density, are presented and discussed in view of the implications for the galaxy formation models. The main results are the lack of substantial evolution of the bright end of the NIR LF and the absence of decline of the luminosity density up to a redshift z ~ 2, implying that most of the stellar population in massive galaxies was already in place at such redshift.Comment: 23 pages, 19 figures. Accepted for publication in A&A. No change

    Quiescent galaxies at z2.5z \gtrsim 2.5: observations vs. models

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    The presence of massive quiescent galaxies at high redshifts is still a challenge for most models of galaxy formation. The aim of this work is to compare the observed number density and properties of these galaxies with the predictions of state-of-the-art models. The sample of massive quiescent galaxies has been selected from the COSMOS2015 photometric catalogue with zphot2.5z_{\rm phot}\geq 2.5, log(M/M)10.5\log (M_*/M_\odot)\geq 10.5 and log(sSFR[yr1])11\log(\mathrm{sSFR\,[yr^{-1}]})\le -11. The photometric SEDs of the selected galaxies have been thoroughly analyzed based on different stellar population synthesis models. The final sample includes only those galaxies qualified as quiescent in all SED fitting runs. The observed properties have been compared to theoretical models: the number density of quiescent galaxies with 10.5log(M/M)<10.810.5 \leq \log(M_*/M_\odot) < 10.8 is reproduced by some models, although there is a large scatter in their predictions. Instead, very massive log(M/M)10.8\log(M_{*}/M_{\odot}) \geq 10.8 are underpredicted by most of the current models of galaxy formation: some of them, built on the CARNage simulation, are consistent with data up to z4z \sim 4, while at higher redshifts the volume of the considered simulation is too small to find such rare objects. Simulated galaxies which match the observed properties in the sSFRM\mathrm{sSFR}-M_* plane at z3z\sim 3 have been analyzed by reconstructing their evolutionary paths: their merger trees suggest that AGN feedback could be the key process allowing for a rapid quenching of the star formation at z4z\gtrsim 4 and that its treatment should be improved in models.Comment: Accepted for publication in ApJL, 9 pages, 6 figure

    Massive and old quiescent galaxies at high redshift

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    Massive quiescent galaxies at high redshift can shed light on the processes of galaxy mass assembly and quenching of the star formation at early epochs. We present observer-frame color-color diagrams designed to identify candidate quiescent galaxies from z=2.5 up to the highest redshifts, that can be then be selected for spectroscopic follow-up observations. The application to the COSMOS2015 catalog shows that, after refining the selection with SED fitting, the number of massive old quiescent galaxies exceeds the forecast of state-of-the-art semi-analytic models, pointing out the need of an improvement of the implemented quenching mechanisms at high redshifts.Comment: Astronomy & Astrophysics, accepted; Matching version in press; 21 pages, 13 figure

    The stellar-to-halo mass relation over the past 12 Gyr

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    Understanding how galaxy properties are linked to the dark matter halos they reside in, and how they co-evolve is a powerful tool to constrain the processes related to galaxy formation. The stellar-to-halo mass relation (SHMR) and its evolution over the history of the Universe provides insights on galaxy formation models and allows to assign galaxy masses to halos in N-body dark matter simulations. We use a statistical approach to link the observed galaxy stellar mass functions on the COSMOS field to dark matter halo mass functions from the DUSTGRAIN simulation and from a theoretical parametrization from z=0 to z=4. We also propose an empirical model to describe the evolution of the stellar-to-halo mass relation as a function of redshift. We calculate the star-formation efficiency (SFE) of galaxies and compare results with previous works and semi-analytical models.Comment: accepted for publication in A&A, matching version in pres

    X-ray redshifts for obscured AGN: a case study in the J1030 deep field

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    We present a procedure to constrain the redshifts of obscured (NH>1022N_H > 10^{22} cm2^{-2}) Active Galactic Nuclei (AGN) based on low-count statistics X-ray spectra, which can be adopted when photometric and/or spectroscopic redshifts are unavailable or difficult to obtain. We selected a sample of 54 obscured AGN candidates on the basis of their X-ray hardness ratio, HR>0.1HR>-0.1, in the Chandra deep field (\sim479 ks, 335 arcmin2^2) around the z=6.3z=6.3 QSO SDSS J1030+0524. The sample has a median value of 80\approx80 net counts in the 0.5-7 keV energy band. We estimate reliable X-ray redshift solutions taking advantage of the main features in obscured AGN spectra, like the Fe 6.4 keV Kα\mathrm{\alpha} emission line, the 7.1 keV Fe absorption edge and the photoelectric absorption cut-off. The significance of such features is investigated through spectral simulations, and the derived X-ray redshift solutions are then compared with photometric redshifts. Both photometric and X-ray redshifts are derived for 33 sources. When multiple solutions are derived by any method, we find that combining the redshift solutions of the two techniques improves the rms by a factor of two. Using our redshift estimates (0.1z40.1\lesssim z \lesssim 4), we derived absorbing column densities in the range 10221024\sim 10^{22}-10^{24} cm2^{-2} and absorption-corrected, 2-10 keV rest-frame luminosities between 1042\sim 10^{42} and 104510^{45} erg s1^{-1}, with median values of NH=1.7×1023N_H = 1.7 \times 10^{23} cm2^{-2} and L210keV=8.3×1043L_{\mathrm{2-10\, keV}} = 8.3\times10^{43} erg s1^{-1}, respectively. Our results suggest that the adopted procedure can be applied to current and future X-ray surveys, for sources detected only in the X-rays or that have uncertain photometric or single-line spectroscopic redshifts.Comment: 22 pages, 18 figure

    The star formation histories of z ∼ 1 post-starburst galaxies

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    Funding: LTA acknowledges support from the Ministry of Higher Education and Scientific Research (MOHESR), Iraq. AW acknowledges financial support from the Royal Society Newton Fund (grant NAF/R1/180403, PI Natalia Vale Asari) and Fundação de à Amparo Pesquisa do Estado de São Paulo (FAPESP) process number 2019/01768-6.We present the star formation histories of 39 galaxies with high-quality rest-frame optical spectra at 0.5 <z <1.3 selected to have strong Balmer absorption lines and/or Balmer break, and compare to a sample of spectroscopically selected quiescent galaxies at the same redshift. Photometric selection identifies a majority of objects that have clear evidence for a recent short-lived burst of star formation within the last 1.5 Gyr, i.e. 'post-starburst' galaxies, however we show that good quality continuum spectra are required to obtain physical parameters such as burst mass fraction and burst age. Dust attenuation appears to be the primary cause for misidentification of post-starburst galaxies, leading to contamination in spectroscopic samples where only the [O II] emission line is available, as well as a small fraction of objects lost from photometric samples. The 31 confirmed post-starburst galaxies have formed 40-90 per cent of their stellar mass in the last1-1.5 Gyr. We use the derived star formation histories to find that the post-starburst galaxies are visible photometrically for 0.5-1 Gyr. This allows us to update a previous analysis to suggest that 25-50 per cent of the growth of the red sequence at z ∼ 1 could be caused by a starburst followed by rapid quenching. We use the inferred maximum historical star formation rates of several 100-1000 M⊙yr-1 and updated visibility times to confirm that sub-mm galaxies are likely progenitors of post-starburst galaxies. The short quenching time-scales of 100-200 Myr are consistent with cosmological hydrodynamic models in which rapid quenching is caused by the mechanical expulsion of gas due to an acive galactic neucleus.Publisher PDFPeer reviewe