The Progenitors of Local Ultra-massive Galaxies Across Cosmic Time: from Dusty Star-bursting to Quiescent Stellar Populations

Using the UltraVISTA catalogs, we investigate the evolution in the 11.4~Gyr since $z=3$ of the progenitors of local ultra-massive galaxies ($\log{(M_{\rm star}/M_{\odot})}\approx11.8$; UMGs), providing a complete and consistent picture of how the most massive galaxies at $z=0$ have assembled. By selecting the progenitors with a semi-empirical approach using abundance matching, we infer a growth in stellar mass of 0.56$^{+0.35}_{-0.25}$ dex, 0.45$^{+0.16}_{-0.20}$~dex, and 0.27$^{+0.08}_{-0.12}$ dex from $z=3$, $z=2$, and $z=1$, respectively, to $z=0$. At $z<1$, the progenitors of UMGs constitute a homogeneous population of only quiescent galaxies with old stellar populations. At $z>1$, the contribution from star-forming galaxies progressively increases, with the progenitors at $2<z<3$ being dominated by massive ($M_{\rm star} \approx 2 \times 10^{11}$M$_{\odot}$), dusty ($A_{\rm V}\sim$1--2.2 mag), star-forming (SFR$\sim$100--400~M$_{\odot}$ yr$^{-1}$) galaxies with a large range in stellar ages. At $z=2.75$, $\sim$15\% of the progenitors are quiescent, with properties typical of post-starburst galaxies with little dust extinction and strong Balmer break, and showing a large scatter in color. Our findings indicate that at least half of the stellar content of local UMGs was assembled at $z>1$, whereas the remaining was assembled via merging from $z\sim 1$ to the present. Most of the quenching of the star-forming progenitors happened between $z=2.75$ and $z=1.25$, in good agreement with the typical formation redshift and scatter in age of $z=0$ UMGs as derived from their fossil records. The progenitors of local UMGs, including the star-forming ones, never lived on the blue cloud since $z=3$. We propose an alternative path for the formation of local UMGs that refines previously proposed pictures and that is fully consistent with our findings.Comment: 20 pages, 15 figures (6 of which in appendix); accepted for publication in the Astrophysical Journa

Spectroscopic Confirmation of an Ultramassive and Compact Galaxy at Z = 3.35: A Detailed Look at an Early Progenitor of Local Giant Ellipticals

We present the first spectroscopic confirmation of an ultra-massive galaxy at redshift z\u3e3 using data from Keck-NIRSPEC, VLT-Xshooter, and GTC-Osiris. We detect strong [OIII] and Lyα emission, and weak [OII], CIV, and HeII, placing C1-23152 at a spectroscopic redshift of zspec=3.351. The modeling of the emission-line corrected spectral energy distribution results in a best-fit stellar mass of M∗=3.1+0.6−0.7×1011M⊙, a star-formation rate of \u3c7 M⊙yr−1, and negligible dust extinction. The stars appear to have formed in a short intense burst ~300-500 Myr prior to the observation epoch, setting the formation redshift of this galaxy at z~4.1. From the analysis of the line ratios and widths, and the observed flux at 24μm, we confirm the presence of a luminous hidden active galactic nucleus (AGN), with bolometric luminosity of ~1046ergs−1. Potential contamination to the observed SED from the AGN continuum is constrained, placing a lower limit on the stellar mass of 2×1011M⊙. HST/WFC3 H160 and ACS I814 images are modeled, resulting in an effective radius of re~1 kpc in the H160 band and a Sersic index n~4.4. This object may be a prototype of the progenitors of local most massive elliptical galaxies in the first 2 Gyr of cosmic history, having formed most of its stars at z\u3e4 in a highly dissipative, intense, and short burst of star formation. C1-23152 is completing its transition to a post-starburst phase while hosting a powerful AGN, potentially responsible for the quenching of the star formation activity

The Rapid Build-up of Massive Early-type Galaxies. Supersolar Metallicity, High Velocity Dispersion and Young Age for an ETG at z=3.35

Thanks to very deep spectroscopic observations carried out at the Large Binocular Telescope, we measured simultaneously stellar age, metallicity and velocity dispersion for C1-23152, an ETG at redshift $z$=3.352, corresponding to an epoch when the Universe was $\sim$1.8 Gyr old. The analysis of its spectrum shows that this galaxy, hosting an AGN, formed and assembled $\sim$2$\times$10$^{11}$ M$_\odot$ shaping its morphology within the $\sim$600 Myr preceding the observations, since $z$$\sim$4.6. The stellar population has a mean mass-weighted age 400$^{+30}_{-70}$ Myr and it is formed between $\sim$600 Myr and $\sim$150 Myr before the observed epoch, this latter being the time since quenching. Its high stellar velocity dispersion, $\sigma_e$=409$\pm$60 km s$^{-1}$, confirms the high mass (M$_{dyn}$=$2.2(\pm0.4)$$\times$10$^{11}$ M$_\odot$) and the high mass density ($\Sigma_e^{M^*}$=$\Sigma_{1kpc}=3.2(\pm0.7)\times10^{10}$ M$_\odot$ kpc$^{-2}$), suggesting a fast dissipative process at its origin. The analysis points toward a supersolar metallicity, [Z/H]=0.25$^{+0.006}_{-0.10}$, in agreement with the above picture, suggesting a star formation efficiency much higher than the replenishment time. However, sub-solar metallicity values cannot be firmly ruled out by our analysis. Quenching must have been extremely efficient to reduce the star formation to SFR$<$6.5 M$_\odot$ yr$^{-1}$ in less than 150 Myr. This could be explained by the presence of the AGN, even if a causal relation cannot be established from the data. C1-23152 has the same stellar and physical properties of the densest ETGs in the local Universe of comparable mass, suggesting that they are C1-23152-like galaxies which evolved to $z=0$ unperturbed.Comment: 20 pages, 12 figures. Accepted for publication in ApJ (revised to match the ApJ version

The evolution in the stellar mass of Brightest Cluster Galaxies over the past 10 billion years

Using a sample of 98 galaxy clusters recently imaged in the near infra-red with the ESO NTT, WIYN and WHT telescopes, supplemented with 33 clusters from the ESO archive, we measure how the stellar mass of the most massive galaxies in the universe, namely Brightest Cluster Galaxies (BCG), increases with time. Most of the BCGs in this new sample lie in the redshift range $0.2<z<0.6$, which has been noted in recent works to mark an epoch over which the growth in the stellar mass of BCGs stalls. From this sample of 132 clusters, we create a subsample of 102 systems that includes only those clusters that have estimates of the cluster mass. We combine the BCGs in this subsample with BCGs from the literature, and find that the growth in stellar mass of BCGs from 10 billion years ago to the present epoch is broadly consistent with recent semi-analytic and semi-empirical models. As in other recent studies, tentative evidence indicates that the stellar mass growth rate of BCGs may be slowing in the past 3.5 billion years. Further work in collecting larger samples, and in better comparing observations with theory using mock images is required if a more detailed comparison between the models and the data is to be made.Comment: 15 pages, 8 tables, 7 figures - Accepted for publication in MNRA

Beyond UVJ: Color Selection of Galaxies in the JWST Era

We present a new rest-frame color-color selection method using "synthetic $u_s-g_s$ and $g_s-i_s$'', $(ugi)_s$ colors to identify star-forming and quiescent galaxies. Our method is similar to the widely-used $U-V$ versus $V-J$ ($UVJ$) diagram. However, $UVJ$ suffers known systematics. Spectroscopic campaigns have shown that $UVJ$-selected quiescent samples at $z \gtrsim 3$ include $\sim 10-30\%$ contamination from galaxies with dust-obscured star formation and strong emission lines. Moreover, at $z>3$, $UVJ$ colors are extrapolated because the rest-frame J-band shifts beyond the coverage of the deepest bandpasses at $< 5~\mu m$ (typically $Spitzer$/IRAC 4.5 $\mu m$ or future $JWST$/NIRCam observations). We demonstrate that $(ugi)_s$ offers improvements to $UVJ$ at $z>3$, and can be applied to galaxies in the $JWST$ era. We apply $(ugi)_s$ selection to galaxies at $0.5<z<6$ from the (observed) 3D-HST and UltraVISTA catalogs, and to the (simulated) JAGUAR catalogs. We show that extrapolation can affect $(V-J)_0$ color by up to 1 magnitude, but changes $(u_s-i_s)_0$ color by $\leq$ 0.2 mag, even at $z\simeq 6$. While $(ugi)_s$-selected quiescent samples are comparable to $UVJ$ in completeness (both achieve $\sim$85-90% at $z=3-3.5$), $(ugi)_s$ reduces contamination in quiescent samples by nearly a factor of two, from $\simeq$35% to $\simeq$17% at $z=3$, and from $\simeq$60% to $\simeq$33% at $z=6$. This leads to improvements in the true-to-false-positive ratio (TP/FP), where we find TP/FP $\gtrsim$ 2.2 for $(ugi)_s$ at $z \simeq 3.5 - 6$, compared to TP/FP $<$ 1 for $UVJ$-selected samples. This indicates that contaminants will outnumber true quiescent galaxies in $UVJ$ at these redshifts, while $(ugi)_s$ will provide higher-fidelity samples.Comment: Submitted to Ap

<i>HST</i> F160W Imaging of Very Massive Galaxies at 1.5 < <i>z</i> < 3.0: Diversity of Structures and the Effect of Close Pairs on Number Density Estimates

We present a targeted follow-up Hubble Space Telescope WFC3 F160W imaging study of very massive galaxies (log(Mstar/M⊙)>11.2) selected from a combination of ground-based near-infrared galaxy surveys (UltraVISTA, NMBS-II, UKIDSS UDS) at 1.5zzz<3.0, however, we find evidence that quiescent galaxies are systematically larger than expected based on the extrapolation of the relation derived using lower stellar mass galaxies. We used the observed light profiles of the blended systems to decompose their stellar masses and investigate the effect of the close pairs on the measured number densities of very massive galaxies in the early universe. We estimate correction factors to account for close-pair blends and apply them to the observed stellar mass functions measured using ground-based surveys. Given the large uncertainties associated with this extreme population of galaxies, there is currently little tension between the (blending-corrected) number density estimates and predictions from theoretical models. Although we currently lack the statistics to robustly correct for close-pair blends, we show that this is a systematic effect which can reduce the observed number density of very massive galaxies by up to a factor of ∼1.5, and should be accounted for in future studies of stellar mass functions

Complete IRAC mapping of the CFHTLS-DEEP, MUSYC AND NMBS-II FIELDS

The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6 and 4.5$\mu$m with the Spitzer Infrared Array Camera (IRAC). The observations cover three Canada-France-Hawaii Telescope Legacy Survey Deep (CFHTLS-D) fields, including one also imaged by AEGIS, and two MUSYC fields. These are then combined with archival data from all previous programs into deep mosaics. The resulting imaging covers a combined area of about 3 $deg^2$, with at least $\sim$2 hr integration time for each field. In this work, we present our data reduction techniques and document the resulting coverage maps at 3.6 and 4.5$\mu$m. All of the images are W-registered to the reference image, which is either the z-band stack image of the 25\% best seeing images from the CFHTLS-D for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images and coverage maps described herein publicly available via the Spitzer Science Center.Comment: Accepted in PASP; released IRAC mosaics available upon publication of the pape

The FENIKS Survey: Spectroscopic Confirmation of Massive Quiescent Galaxies at z ~ 3-5

The measured ages of massive, quiescent galaxies at $z\sim 3-4$ imply that massive galaxies quench as early as $z\sim 6$. While the number of spectroscopic confirmations of quiescent galaxies at $z < 3$ has increased over the years, there are only a handful at $z > 3.5$. We report spectroscopic redshifts of one secure ($z=3.757$) and two tentative ($z = 3.336$, $z=4.673$) massive ($\log(M_\ast/M_\odot) > 10.3$) quiescent galaxies with 11 hours of Keck/MOSFIRE $K$-band observations. Our candidates were selected from the FENIKS survey, which uses deep Gemini/Flamingos-2 $K_b$ $K_r$ imaging optimized for increased sensitivity to the characteristic red colors of galaxies at $z > 3$ with strong Balmer/4000 \AA\ breaks. The rest-frame $UVJ$ and $(ugi)_s$ colors of 3/4 quiescent candidates are consistent with $1-2$ Gyr old stellar populations. This places these galaxies as the oldest objects at these redshifts, and challenges the notion that quiescent galaxies at $z > 3$ are all recently-quenched, "post-starburst'' galaxies. Our spectroscopy shows that the other quiescent-galaxy candidate is a broad-line AGN ($z = 3.594$) with strong, redshifted $H\beta$+[O III] emission with a velocity offset $>1000$ km/s, indicative of a powerful outflow. The star-formation history of our highest redshift candidate suggests that its progenitor was already in place by $z \sim 7-11$, reaching $\sim$ 10$^{11} M_{\odot}$ by $z \simeq 10$. These observations reveal the limit of what is possible with deep near-infrared photometry and targeted spectroscopy from the ground and demonstrate that secure spectroscopic confirmation of quiescent galaxies at $z > 4$ is only feasible with JWST.Comment: 20 pages, 11 figures, submitted to Ap

Spectroscopic confirmation of an ultramassive and compact galaxy at Z=3.35: A detailed look at an early progenitor of local giant ellipticals

et al.We present the first spectroscopic confirmation of an ultramassive galaxy at redshift z > 3 using data from Keck- NIRSPEC, VLT-X-shooter, and GTC-Osiris. We detect strong [O III] and Lyα emission, and weak [O II], C IV, and He II, placing C1-23152 at a spectroscopic redshift of zspec = 3.351. The modeling of the emission-line-corrected spectral energy distribution (SED) results in a best-fit stellar mass of M∗ = 3.1-0.7 +0.6 × 1011 M⊙, a star formation rate of 4 in a highly dissipative, intense, and short burst of star formation. C1-23152 is completing its transition to a post-starburst phase while hosting a powerful AGN, potentially responsible for the quenching of the star formation activity.This work was supported through NSF ATI grants 1020981 and 1106284.Peer Reviewe