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 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

SXDF-ALMA 1.5 arcmin^2 deep survey. A compact dusty star-forming galaxy at z=2.5

We present first results from the SXDF-ALMA 1.5 arcmin^2 deep survey at 1.1 mm using Atacama Large Millimeter Array (ALMA). The map reaches a 1sigma depth of 55 uJy/beam and covers 12 Halpha-selected star-forming galaxies at z = 2.19 or z=2.53. We have detected continuum emission from three of our Halpha-selected sample, including one compact star-forming galaxy with high stellar surface density, NB2315-07. They are all red in the rest-frame optical and have stellar masses of log (M*/Msun)>10.9 whereas the other blue, main-sequence galaxies with log(M*/Msun)=10.0-10.8 are exceedingly faint, <290 uJy (2sigma upper limit). We also find the 1.1 mm-brightest galaxy, NB2315-02, to be associated with a compact (R_e=0.7+-0.1 kpc), dusty star-forming component. Given high gas fraction (44^{+20}_{-8}% or 37^{+25}_{-3}%) and high star formation rate surface density (126^{+27}_{-30} Msun yr^{-1}kpc^{-2}), the concentrated starburst can within less than 50^{+12}_{-11} Myr build up a stellar surface density matching that of massive compact galaxies at z~2, provided at least 19+-3% of the total gas is converted into stars in the galaxy centre. On the other hand, NB2315-07, which already has such a high stellar surface density core, shows a gas fraction (23+-8%) and is located in the lower envelope of the star formation main-sequence. This compact less star-forming galaxy is likely to be in an intermediate phase between compact dusty star-forming and quiescent galaxies.Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ

JWSTJWST Insight Into a Lensed HSTHST-dark Galaxy and its Quiescent Companion at z=2.58z=2.58

Using the novel $JWST$/NIRCam observations in the Abell 2744 field, we present a first spatially resolved overview of an $HST$-dark galaxy, spectroscopically confirmed at $z=2.58$ with magnification $\mu\approx1.9$. While being largely invisible at $\sim$1 $\mu$m with NIRCam, except for sparse clumpy sub-structures, the object is well-detected and resolved in the long-wavelength bands with a spiral shape clearly visible in F277W. By combining ancillary ALMA and $Herschel$ data, we infer that this object is an edge-on dusty spiral with an intrinsic stellar mass log$(M_*/M_\odot)\sim11.3$ and a dust-obscured SFR$\sim 300~M_\odot$~yr$^{-1}$. A massive quiescent galaxy (log$(M_*/M_\odot)\sim10.8$) with tidal features lies 2\farcs{0} away ($r$$\sim$9 kpc), at a consistent redshift as inferred by $JWST$ photometry, indicating a potential major merger. The dusty spiral lies on the main-sequence of star formation, and shows high dust attenuation in the optical ($3<A_{\rm V}<4.5$). In the far-infrared, its integrated dust SED is optically thick up to $\lambda_0 \sim 500$ $\mu$m, further supporting the extremely dusty nature. Spatially resolved analysis of the $HST$-dark galaxy reveals a largely uniform $A_{\rm V}\sim 4$ area spanning $\sim$57 kpc$^2$, which spatially matches to the ALMA 1 mm continuum emission. Accounting for the surface brightness dimming and the depths of current $JWST$ surveys, unlensed analogs of the $HST$-dark galaxy at $z>4$ would be only detectable in F356W and F444W in UNCOVER-like survey, and become totally $JWST$-dark at $z\sim6$. This suggests that detecting highly attenuated galaxies in the Epoch of Reionization might be a challenging task for $JWST$.Comment: 15 pages, 5 figures, 1 table. Accepted to ApJ

Compact starbursts in z~3-6 submillimeter galaxies revealed by ALMA

We report the source size distribution, as measured by ALMA millimetric continuum imaging, of a sample of 13 AzTEC-selected submillimeter galaxies (SMGs) at z_photo ~ 3-6. Their infrared luminosities and star-formation rates (SFR) are L_IR ~ 2-6 x 10^12 L_sun and ~ 200-600 M_sun yr-1, respectively. The size of z ~ 3-6 SMGs ranges from 0".10 to 0".38 with a median of 0".20+0".03-0".05 (FWHM), corresponding to a median circularized effective radius (Rc,e) of 0.67+0.13-0.14 kpc, comparable to the typical size of the stellar component measured in compact quiescent galaxies at z ~ 2 (cQGs) --- R ~ 1 kpc. The median surface SFR density of our z ~ 3-6 SMGs is 100+42-26 M_sun yr-1 kpc-2, comparable to that seen in local merger-driven (U)LIRGsrather than in extended disk galaxies at low and high redshifts. The discovery of compact starbursts in z >~ 3 SMGs strongly supports a massive galaxy formation scenario wherein z ~ 3-6 SMGs evolve into the compact stellar components of z ~ 2 cQGs. These cQGs are then thought to evolve into the most massive ellipticals in the local Universe, mostly via dry mergers. Our results thus suggest that z >~ 3 SMGs are the likely progenitors of massive local ellipticals, via cQGs, meaning that we can now trace the evolutionary path of the most massive galaxies over a period encompassing ~ 90% of the age of the Universe.Comment: 12 pages, 10 figures, accepted to the Astrophysical Journal part