The role of extremely red galaxies in the history of structure formation

In this thesis we investigate the redshift distribution and derived cosmological properties of Extremely Red Galaxies (ERGs), through the study of a sample selected with Ks ≤ 22 and (I₇₇₅ - Ks) > 3.92 (Vega) in 50.4 arcmin² of the GOODS/CDFS field. We also study the properties of the total parent sample of Ks-selected galaxies in the same field, with the aim of understanding their evolution and clarifying the role of ERGs within this population. We determine that the bright end of the Ks-band luminosity function, which is progressively well reproduced by the ERGs with increasing redshift, shows no sign of decline up to at least redshift z ~ 2.5. We also explore the evolution of massive systems present in our sample: ~ 20% - 25% of the population of local galaxies with assembled stellar mass M > 1 x 10¹¹M⨀ were formed before redshift z ~ 4, and contain ~ 45% to 70% of the stellar mass density of the Universe at that redshift. Within our sample, the comoving number density of these massive systems is then essentially constant down to redshift z ~ 1.5. The remaining massive systems observed in the local Universe are assembled later, at redshifts z < 1.5. Thus, a two-fold assembly history for massive galaxies is suggested, in which galaxy/star formation proceeds very efficiently in high mass haloes at very high redshift. It is the massive ERGs at redshift z > 1 which contain the imprints of the most efficient period of galaxy formation. Finally, from the morphological study of our galaxies with estimated mass M > 10¹¹M⨀ and redshifts z < 2, we explore the bridge between massive ERGs at z > 1 and local massive galaxies. ~ 50% - 60% of all the massive galaxies at 0.5 ≲ z ≲ 2.0 have surface brightness profiles close to a de Vaucouleurs law. All our results are consistent with a scenario in which the most massive ERGs are the progenitors of local cluster elliptical/SO galaxies

No need for extreme stellar masses at z~7: a test-case study for COS-87259

Recent controversy regarding the existence of massive ($\log(M_*/M_\odot) \gtrsim 11$) galaxies at $z>6$ is posing a challenge for galaxy formation theories. Hence, it is of critical importance to understand the effects of SED fitting methods on stellar mass estimates of Epoch of Re-ionisation galaxies. In this work, we perform a case study on the AGN-host galaxy candidate COS-87259 with spectroscopic redshift $z_{\rm spec}=6.853$, that is claimed to have an extremely high stellar mass of $\log(M_*/M_\odot) \sim 11.2$. We test a suite of different SED fitting algorithms and stellar population models on our independently measured photometry in 17 broad bands for this source. Between five different code set-ups, the stellar mass estimates for COS-87259 span $\log(M_*/M_\odot) = 10.24$--11.00, whilst the reduced $\chi^2$ values of the fits are all close to unity within $\Delta\chi^2_\nu=0.9$, so that the quality of the SED fits is basically indistinguishable. Only the Bayesian inference code Prospector using a non-parametric star formation history model yields a stellar mass exceeding $\log(M_*/M_\odot)=11$. As this SED fitting prescription is becoming increasingly popular for James Webb Space Telescope high-redshift science, we stress the absolute importance to test various SED fitting routines particularly on apparently very massive galaxies at such high redshifts. Ultimately, we conclude that the extremely high stellar mass estimate for COS-87259 is not necessary, deriving equally good fits with stellar masses $\sim 1$ dex lower.Comment: Submitted to ApJ

ALMA Millimeter/Submillimeter Sources among Spitzer SMUVS Galaxies at z &gt; 2 in the COSMOS Field

Submillimeter observations reveal the star formation activity obscured by dust in the young Universe. It still remains unclear how galaxies detected at submillimeter wavelengths are related to ultraviolet/optical-selected galaxies in terms of their observed quantities, physical properties, and evolutionary stages. Deep near- and mid-infrared observational data are crucial to characterize the stellar properties of galaxies detected with submillimeter emission. In this study, we make use of a galaxy catalog from the Spitzer Matching survey of the UltraVISTA ultra-deep Stripes. By crossmatching with a submillimeter source catalog constructed with archival data of the Atacama Large Millimeter/submillimeter Array (ALMA), we search for galaxies at z &gt; 2 with a submillimeter detection in our galaxy catalog. We find that the ALMA-detected galaxies at z &gt; 2 are systematically massive and have redder K s -[4.5] colors than the nondetected galaxies. The redder colors are consistent with the larger dust reddening values of the ALMA-detected galaxies obtained from spectral energy distribution (SED) fitting. We also find that the ALMA-detected galaxies tend to have brighter 4.5 μm magnitudes. This may suggest that they tend to have smaller mass-to-light ratios and thus to be younger than star-forming galaxies fainter at submillimeter wavelengths with similar stellar masses. We identify starburst galaxies with high specific star formation rates among both ALMA-detected and nondetected SMUVS sources. Irrespective of their brightness at submillimeter wavelengths, these populations have similar dust reddening values, which may suggest a variety of dust SED shapes among the starburst galaxies at z &gt; 2.</p

ALMA sub-/millimeter sources among SpitzerSpitzer SMUVS galaxies at z>2z>2 in the COSMOS field

Sub-millimeter observations reveal the star-formation activity obscured by dust in the young Universe. It still remains unclear how galaxies detected at sub-millimeter wavelengths are related to ultraviolet/optical-selected galaxies in terms of their observed quantities, physical properties, and evolutionary stages. Deep near- and mid-infrared observational data are crucial to characterize the stellar properties of galaxies detected with sub-millimeter emission. In this study, we make use of a galaxy catalog from the $Spitzer$ Matching Survey of the UltraVISTA ultra-deep Stripes. By cross-matching with a sub-millimeter source catalog constructed with the archival data of the Atacama Large Millimeter/submillimeter Array (ALMA), we search for galaxies at $z>$ 2 with a sub-millimeter detection in our galaxy catalog. We find that the ALMA-detected galaxies at $z>$ 2 are systematically massive and have redder $K_s$-[4.5] colors than the non-detected galaxies. The redder colors are consistent with the larger dust reddening values of the ALMA-detected galaxies obtained from SED fitting. We also find that the ALMA-detected galaxies tend to have brighter 4.5 $\mu$m magnitudes. This may suggest that they tend to have smaller mass-to-light ratios, and thus, to be younger than star-forming galaxies fainter at sub-millimeter wavelengths with similar stellar masses. We identify starburst galaxies with high specific star-formation rates among both ALMA-detected and non-detected SMUVS sources. Irrespective of their brightness at sub-millimeter wavelengths, these populations have similar dust reddening values, which may suggest a variety of dust SED shapes among the starburst galaxies at $z>2$.Comment: 14 pages, 7 figures, 2 tables, Accepted for publication in Ap

ALMA Millimeter/Submillimeter Sources among Spitzer SMUVS Galaxies at z &gt; 2 in the COSMOS Field

Submillimeter observations reveal the star formation activity obscured by dust in the young Universe. It still remains unclear how galaxies detected at submillimeter wavelengths are related to ultraviolet/optical-selected galaxies in terms of their observed quantities, physical properties, and evolutionary stages. Deep near- and mid-infrared observational data are crucial to characterize the stellar properties of galaxies detected with submillimeter emission. In this study, we make use of a galaxy catalog from the Spitzer Matching survey of the UltraVISTA ultra-deep Stripes. By crossmatching with a submillimeter source catalog constructed with archival data of the Atacama Large Millimeter/submillimeter Array (ALMA), we search for galaxies at z &gt; 2 with a submillimeter detection in our galaxy catalog. We find that the ALMA-detected galaxies at z &gt; 2 are systematically massive and have redder K s -[4.5] colors than the nondetected galaxies. The redder colors are consistent with the larger dust reddening values of the ALMA-detected galaxies obtained from spectral energy distribution (SED) fitting. We also find that the ALMA-detected galaxies tend to have brighter 4.5 μm magnitudes. This may suggest that they tend to have smaller mass-to-light ratios and thus to be younger than star-forming galaxies fainter at submillimeter wavelengths with similar stellar masses. We identify starburst galaxies with high specific star formation rates among both ALMA-detected and nondetected SMUVS sources. Irrespective of their brightness at submillimeter wavelengths, these populations have similar dust reddening values, which may suggest a variety of dust SED shapes among the starburst galaxies at z &gt; 2.</p

ALMA Millimeter/Submillimeter Sources among Spitzer SMUVS Galaxies at z &gt; 2 in the COSMOS Field

Submillimeter observations reveal the star formation activity obscured by dust in the young Universe. It still remains unclear how galaxies detected at submillimeter wavelengths are related to ultraviolet/optical-selected galaxies in terms of their observed quantities, physical properties, and evolutionary stages. Deep near- and mid-infrared observational data are crucial to characterize the stellar properties of galaxies detected with submillimeter emission. In this study, we make use of a galaxy catalog from the Spitzer Matching survey of the UltraVISTA ultra-deep Stripes. By crossmatching with a submillimeter source catalog constructed with archival data of the Atacama Large Millimeter/submillimeter Array (ALMA), we search for galaxies at z &gt; 2 with a submillimeter detection in our galaxy catalog. We find that the ALMA-detected galaxies at z &gt; 2 are systematically massive and have redder K s -[4.5] colors than the nondetected galaxies. The redder colors are consistent with the larger dust reddening values of the ALMA-detected galaxies obtained from spectral energy distribution (SED) fitting. We also find that the ALMA-detected galaxies tend to have brighter 4.5 μm magnitudes. This may suggest that they tend to have smaller mass-to-light ratios and thus to be younger than star-forming galaxies fainter at submillimeter wavelengths with similar stellar masses. We identify starburst galaxies with high specific star formation rates among both ALMA-detected and nondetected SMUVS sources. Irrespective of their brightness at submillimeter wavelengths, these populations have similar dust reddening values, which may suggest a variety of dust SED shapes among the starburst galaxies at z &gt; 2.</p

ALMA Millimeter/Submillimeter Sources among Spitzer SMUVS Galaxies at z &gt; 2 in the COSMOS Field

Submillimeter observations reveal the star formation activity obscured by dust in the young Universe. It still remains unclear how galaxies detected at submillimeter wavelengths are related to ultraviolet/optical-selected galaxies in terms of their observed quantities, physical properties, and evolutionary stages. Deep near- and mid-infrared observational data are crucial to characterize the stellar properties of galaxies detected with submillimeter emission. In this study, we make use of a galaxy catalog from the Spitzer Matching survey of the UltraVISTA ultra-deep Stripes. By crossmatching with a submillimeter source catalog constructed with archival data of the Atacama Large Millimeter/submillimeter Array (ALMA), we search for galaxies at z &gt; 2 with a submillimeter detection in our galaxy catalog. We find that the ALMA-detected galaxies at z &gt; 2 are systematically massive and have redder K s -[4.5] colors than the nondetected galaxies. The redder colors are consistent with the larger dust reddening values of the ALMA-detected galaxies obtained from spectral energy distribution (SED) fitting. We also find that the ALMA-detected galaxies tend to have brighter 4.5 μm magnitudes. This may suggest that they tend to have smaller mass-to-light ratios and thus to be younger than star-forming galaxies fainter at submillimeter wavelengths with similar stellar masses. We identify starburst galaxies with high specific star formation rates among both ALMA-detected and nondetected SMUVS sources. Irrespective of their brightness at submillimeter wavelengths, these populations have similar dust reddening values, which may suggest a variety of dust SED shapes among the starburst galaxies at z &gt; 2.</p

Deep GMOS Spectroscopy of Extremely Red Galaxies in GOODS-South: Ellipticals, Mergers and Red Spirals at 1<z<2

We have performed a deep spectroscopic survey of extremely red galaxies on the GOODS-South field, using GMOS on Gemini South. We present here spectra and redshifts for 16 ERGs at 0.87<z<2.02, to a limit K=20.2. The ERHs are a mixture of spheroidals, mergers and spirals, with one AGN. For at least 10 of these galaxies we observe [OII] emission lines. We perform an age-dating analysis by fitting the spectra and 9-band photometry of the ERGs with models of passively evolving stellar populations combined with a younger star-forming component. The best-fitting ages for the old stellar components range from 0.6 to 4.5 Gyr, with a mean 2.1 Gyr. Masses range from 3 to 20 times 10^10 solar masses. The star-forming component typically forms a few per cent of the total mass, with dust reddening averaging E(B-V)=0.35. Its timescale tends to be short for mergers (<50 Myr) and longer (200-800 Myr) for spiral ERGs.Comment: 19 pages, 9 figure

The Galaxy Starburst/Main-sequence Bimodality over Five Decades in Stellar Mass at z ≈ 3–6.5

We study the relation between stellar mass (M*) and star formation rate (SFR) for star-forming galaxies over approximately five decades in stellar mass (5.5 <~ log10(M*/Msun) <~ 10.5) at z ~ 3-6.5. This unprecedented coverage has been possible thanks to the joint analysis of blank non-lensed fields (COSMOS/SMUVS) and cluster lensing fields (Hubble Frontier Fields) which allow us to reach very low stellar masses. Previous works have revealed the existence of a clear bimodality in the SFR-M* plane with a star-formation Main Sequence and a starburst cloud at z ~ 4-5. Here we show that this bimodality extends to all star-forming galaxies and is valid in the whole redshift range z ~ 3-6.5. We find that starbursts constitute at least 20% of all star-forming galaxies with M* >~ 10^9 Msun at these redshifts and reach a peak of 40% at z=4-5. More importantly, 60% to 90% of the total SFR budget at these redshifts is contained in starburst galaxies, indicating that the starburst mode of star-formation is dominant at high redshifts. Almost all the low stellar-mass starbursts with log10(M*/Msun) <~ 8.5 have ages comparable to the typical timescales of a starburst event, suggesting that these galaxies are being caught in the process of formation. Interestingly, galaxy formation models fail to predict the starburst/main-sequence bimodality and starbursts overall, suggesting that the starburst phenomenon may be driven by physical processes occurring at smaller scales than those probed by these models.Comment: 24 pages, including 15 figures (17 files in total) and 4 tables. The manuscript has been accepted for publication in the Ap

The mass, colour, and structural evolution of today's massive galaxies since z~5

In this paper, we use stacking analysis to trace the mass-growth, colour evolution, and structural evolution of present-day massive galaxies ($\log(M_{*}/M_{\odot})=11.5$) out to $z=5$. We utilize the exceptional depth and area of the latest UltraVISTA data release, combined with the depth and unparalleled seeing of CANDELS to gather a large, mass-selected sample of galaxies in the NIR (rest-frame optical to UV). Progenitors of present-day massive galaxies are identified via an evolving cumulative number density selection, which accounts for the effects of merging to correct for the systematic biases introduced using a fixed cumulative number density selection, and find progenitors grow in stellar mass by $\approx1.5~\mathrm{dex}$ since $z=5$. Using stacking, we analyze the structural parameters of the progenitors and find that most of the stellar mass content in the central regions was in place by $z\sim2$, and while galaxies continue to assemble mass at all radii, the outskirts experience the largest fractional increase in stellar mass. However, we find evidence of significant stellar mass build up at $r4$ probing an era of significant mass assembly in the interiors of present day massive galaxies. We also compare mass assembly from progenitors in this study to the EAGLE simulation and find qualitatively similar assembly with $z$ at $r<3~\mathrm{kpc}$. We identify $z\sim1.5$ as a distinct epoch in the evolution of massive galaxies where progenitors transitioned from growing in mass and size primarily through in-situ star formation in disks to a period of efficient growth in $r_{e}$ consistent with the minor merger scenario.Comment: 19 pages, 14 figures, accepted for publicatio