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Register a new userEmergence of an Ultra-Red Ultra-Massive Galaxy Cluster Core at $z=4$
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Recent simulations and observations of massive galaxy cluster evolution predict that the majority of stellar mass build up happens within cluster members by $z=2$, before cluster virialization. Protoclusters rich with dusty, star-forming galaxies (DSFGs) at $z>3$ are the favored candidate progenitors for these massive galaxy clusters at $zsim0$. We present here the first study analyzing stellar emission along with cold dust and gas continuum emission in a spectroscopically confirmed $z=4.002$ protocluster core rich with DSFGs, the Distant Red Core (DRC). We combine new HST and Spitzer data with existing Gemini, Herschel, and ALMA observations to derive individual galaxy-level properties, and compare them to coeval field and other protocluster galaxies. All of the protocluster members are massive ($>10^{10}$ M$_odot$), but not significantly more so than their coeval field counterparts. Within uncertainty, all are nearly indistinguishable from galaxies on the star-forming vs. stellar mass main-sequence relationship, and on the star formation efficiency plane. Assuming no future major influx of fresh gas, we estimate that these gaseous DSFGs will deplete their gas reservoirs in $sim300$ Myr, becoming the massive quiescent ellipticals dominating cluster cores by $zsim3$. Using various methodologies, we derive a total $z=4$ halo mass of $sim10^{14}$ M$_odot$, and estimate that the DRC will evolve to become an ultra-massive cluster core of mass $gtrsim10^{15}$ M$_odot$ by $z=0$.
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We present the first spectroscopic confirmation of an ultra-massive galaxy at redshift z>3 using data from Keck-NIRSPEC, VLT-Xshooter, and GTC-Osiris. We detect strong [OIII] and Ly$alpha$ emission, and weak [OII], CIV, and HeII, placing C1-23152 at a spectroscopic redshift of $z_{spec}$=3.351. The modeling of the emission-line corrected spectral energy distribution results in a best-fit stellar mass of $M_{*}=3.1^{+0.6}_{-0.7}times10^{11} M_{odot}$, a star-formation rate of <7 $M_{odot} yr^{-1}$, 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 24$mu$m, we confirm the presence of a luminous hidden active galactic nucleus (AGN), with bolometric luminosity of ~$10^{46}erg s^{-1}$. Potential contamination to the observed SED from the AGN continuum is constrained, placing a lower limit on the stellar mass of $2times10^{11} M_{odot}$. HST/WFC3 $H_{160}$ and ACS $I_{814}$ images are modeled, resulting in an effective radius of $r_{e}$~1 kpc in the $H_{160}$ 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>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.
We report on the properties of the most massive ultra-compact dwarf galaxy (UCD) in the nearby Virgo Cluster of galaxies using imaging from the Next Generation Virgo Cluster Survey (NGVS) and spectroscopy from Keck/DEIMOS. This object (M59-UCD3) appears to be associated with the massive Virgo galaxy M59 (NGC 4621), has an integrated velocity dispersion of 78 km/s, a dynamical mass of $3.7times10^8 M_odot$, and an effective radius ($R_e$) of 25 pc. With an effective surface mass density of $9.4times10^{10} M_odot/kpc^2$, it is the densest galaxy in the local Universe discovered to date, surpassing the density of the luminous Virgo UCD, M60-UCD1. M59-UCD3 has a total luminosity of $M_{g}=-14.2$ mag, and a spectral energy distribution consistent with an old (14 Gyr) stellar population with [Fe/H]=0.0 and [$alpha$/Fe]=+0.2. We also examine deep imaging around M59 and find a broad low surface brightness stream pointing towards M59-UCD3, which may represent a tidal remnant of the UCD progenitor. This UCD, along with similar objects like M60-UCD1 and M59cO, likely represents an extreme population of tidally stripped galaxies more akin to larger and more massive compact early-type galaxies than to nuclear star clusters in present-day dwarf galaxies.
Using spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS) we report here on the discovery of PCl J1001+0220, a massive proto-cluster located at $z_{spec}sim4.57$ in the COSMOS field. The proto-cluster was initially detected as a $sim12sigma$ overdensity of typical star-forming galaxies in the blind spectroscopic survey of the early universe ($2<z<6$) performed by VUDS. It was further mapped using a new technique developed that statistically combines spectroscopic and photometric redshifts, the latter derived from a recent compilation of deep multi-band imaging. Through various methods, the descendant halo mass of PCl J1001+0220 is estimated to be $log(M_{h}/M_{odot})_{z=0}sim14.5-15$ with a large amount of mass apparently already in place at $zsim4.57$. Tentative evidence is found for a fractional excess of older and more massive galaxies within the proto-cluster, an observation which suggests the pervasive early onset of vigorous star formation. No evidence is found for the differences in the star formation rates of member and a matched sample of coeval field galaxies either through rest-frame ultraviolet methods or through stacking extremely deep Very Large Array 3 GHz imaging. Additionally, no evidence for pervasive strong active galactic nuclei (AGN) activity is observed. Analysis of Hubble Space Telescope images provides weak evidence for for an elevated incidence of galaxy-galaxy interaction within the proto-cluster. The spectral properties of the two samples are compared, with a definite suppression of Ly$alpha$ seen in the average member galaxy relative to the coeval field ($f_{esc,Lyalpha}=1.8^{+0.3}_{-1.7}$% and $4.0^{+1.0}_{-0.8}$%, respectively). This observation along with other lines of evidence leads us to infer the possible presence of a large, cool diffuse medium within the proto-cluster environment evocative of a nascent intracluster medium.
We present the results of a pilot near-infrared (NIR) spectroscopic campaign of five very massive galaxies ($log(text{M}_star/text{M}_odot)>11.45$) in the range of $1.7<z<2.7$. We measure an absorption feature redshift for one galaxy at $z_text{spec}=2.000pm0.006$. For the remaining galaxies, we combine the photometry with the continuum from the spectra to estimate continuum redshifts and stellar population properties. We define a continuum redshift ($z_{rm cont}$ ) as one in which the redshift is estimated probabilistically using EAZY from the combination of catalog photometry and the observed spectrum. We derive the uncertainties on the stellar population synthesis properties using a Monte Carlo simulation and examine the correlations between the parameters with and without the use of the spectrum in the modeling of the spectral energy distributions (SEDs). The spectroscopic constraints confirm the extreme stellar masses of the galaxies in our sample. We find that three out of five galaxies are quiescent (star formation rate of $lesssim 1 M_odot~yr^{-1}$) with low levels of dust obscuration ($A_{rm V} < 1$) , that one galaxy displays both high levels of star formation and dust obscuration (${rm SFR} approx 300 M_odot~{rm yr}^{-1}$, $A_{rm V} approx 1.7$~mag), and that the remaining galaxy has properties that are intermediate between the quiescent and star-forming populations.
Ultra diffuse galaxies (UDGs) have the sizes of giant galaxies but the luminosities of dwarfs. A key to understanding their origins comes from their total masses, but their low surface brightnesses ($mu(V) geq$ 25.0) generally prohibit dynamical studies. Here we report the first such measurements for a UDG (VCC~1287 in the Virgo cluster), based on its globular cluster system dynamics and size. From 7 GCs we measure a mean systemic velocity $v_{rm sys}$ = 1071$^{+14}_{-15}$ km/s, thereby confirming a Virgo-cluster association. We measure a velocity dispersion of 33$^{+16}_{-10}$ km/s within 8.1 kpc, corresponding to an enclosed mass of $(4.5 pm 2.8)times10^{9}$ $M_{odot}$ and a $g$-band mass-to-light ratio of $(M/L)_g = 106^{+126}_{-54}$. From the cumulative mass curve, along with the GC numbers, we estimate a virial mass of $sim8times10^{10}$ $M_{odot}$, yielding a dark-to-stellar mass fraction of $sim3000$. We show that this UDG is an outlier in $M_{rm star} - M_{rm halo}$ relations, suggesting extreme stochasticity in relatively massive star-forming halos in clusters. Finally, we discuss how counting GCs offers an efficient route to determining virial masses for UDGs.
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