Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpectroscopic Confirmation of a Protocluster at $z=3.37$ with a High Fraction of Quiescent Galaxies
309
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the discovery of MAGAZ3NE J095924+022537, a spectroscopically-confirmed protocluster at $z = 3.3665^{+0.0009}_{-0.0012}$ around a spectroscopically-confirmed $UVJ$-quiescent ultra-massive galaxy (UMG; $M_{star}=2.34^{+0.23}_{-0.34}times10^{11} {rm M}_odot$) in the COSMOS UltraVISTA field. We present a total of 38 protocluster members (14 spectroscopic and 24 photometric), including the UMG. Notably, and in marked contrast to protoclusters previously reported at this epoch which have been found to contain predominantly star-forming members, we measure an elevated fraction of quiescent galaxies relative to the coeval field ($73.3^{+26.7}_{-16.9}%$ versus $11.6^{+7.1}_{-4.9}%$ for galaxies with stellar mass $M_{star} geq 10^{11} {rm M}_odot$). This high quenched fraction provides a striking and important counterexample to the seeming ubiquitousness of star-forming galaxies in protoclusters at $z>2$ and suggests, rather, that protoclusters exist in a diversity of evolutionary states in the early Universe. We discuss the possibility that we might be observing either early mass quenching or non-classical environmental quenching. We also present the discovery of MAGAZ3NE J100028+023349, a second spectroscopically-confirmed protocluster, at a very similar redshift of $z = 3.3801^{+0.0213}_{-0.0281}$. We present a total of 20 protocluster members, 12 of which are photometric and 8 spectroscopic including a post-starburst UMG ($M_{star}=2.95^{+0.21}_{-0.20}times10^{11} {rm M}_odot$). Protoclusters MAGAZ3NE J0959 and MAGAZ3NE J1000 are separated by 18 arcminutes on the sky (35 comoving Mpc), in good agreement with predictions from simulations for the size of Coma-type cluster progenitors at this epoch. It is highly likely that the two UMGs are the progenitors of Brightest Cluster Galaxies (BCGs) seen in massive virialized clusters at lower redshift.
rate research
Read More
We present the analysis and results of a spectroscopic follow-up program of a mass-selected sample of six galaxies at 3 < z < 4 using data from Keck-NIRSPEC and VLT-Xshooter. We confirm the z > 3 redshifts for half of the sample through the detection of strong nebular emission lines, and improve the zphot accuracy for the remainder of the sample through the combination of photometry and spectra. The modeling of the emission-line-corrected spectral energy distributions (SEDs) adopting improved redshifts confirms the very large stellar masses of the sample (M_* ~ 1.5-4 x 10^11 Msun) in the first 2 Gyrs of cosmic history, with a diverse range in stellar ages, star formation rates and dust content. From the analysis of emission line luminosities and widths, and far-infrared (FIR) fluxes we confirm that >80% of the sample are hosts to luminous hidden active galactic nuclei (AGNs), with bolometric luminosities of ~10^(44-46) erg/s. We find that the MIPS 24um photometry is largely contaminated by AGN continuum, rendering the SFRs derived using only 24um photometry to be severely overestimated. By including the emission from the AGN in the modeling of the UV-to-FIR SEDs, we confirm that the presence of the AGN does not bias considerably the stellar masses (< 0.3 dex at 1sigma). We show evidence for a rapid increase of the AGN fraction from ~30% to ~60-100% over the 1 Gyr between z~2 and z~3. Although we cannot exclude some enhancement of the AGN fraction for our sample due to selection effects, the small measured [OIII] contamination to the observed K-band fluxes suggests that our sample is not significantly biased toward massive galaxies hosting AGNs.
We report a massive quiescent galaxy at $z_{rm spec}=3.0922^{+0.008}_{-0.004}$ spectroscopically confirmed at a protocluster in the SSA22 field by detecting the Balmer and Ca {footnotesize II} absorption features with multi-object spectrometer for infrared exploration (MOSFIRE) on the Keck I telescope. This is the most distant quiescent galaxy confirmed in a protocluster to date. We fit the optical to mid-infrared photometry and spectrum simultaneously with spectral energy distribution (SED) models of parametric and nonparametric star formation histories (SFH). Both models fit the observed SED well and confirm that this object is a massive quiescent galaxy with the stellar mass of $log(rm M_{star}/M_{odot}) = 11.26^{+0.03}_{-0.04}$ and $11.54^{+0.03}_{-0.00}$, and star formation rate of $rm SFR/M_{odot}~yr^{-1} <0.3$ and $=0.01^{+0.03}_{-0.01}$ for parametric and nonparametric models, respectively. The SFH from the former modeling is described as an instantaneous starburst while that of the latter modeling is longer-lived but both models agree with a sudden quenching of the star formation at $sim0.6$ Gyr ago. This massive quiescent galaxy is confirmed in an extremely dense group of galaxies predicted as a progenitor of a brightest cluster galaxy formed via multiple mergers in cosmological numerical simulations. We newly find three plausible [O III]$lambda$5007 emitters at $3.0791leq z_{rm spec}leq3.0833$ happened to be detected around the target. Two of them just between the target and its nearest massive galaxy are possible evidence of their interactions. They suggest the future strong size and stellar mass evolution of this massive quiescent galaxy via mergers.
We report the spectroscopic confirmation of a new protocluster in the COSMOS field at $z$ $sim$ 2.2, COSMOS Cluster 2.2 (CC2.2), originally identified as an overdensity of narrowband selected H$alpha$ emitting candidates. With only two masks of Keck/MOSFIRE near-IR spectroscopy in both $H$ ($sim$ 1.47-1.81 $mu$m) and $K$ ($sim$ 1.92-2.40 $mu$m) bands ($sim$ 1.5 hour each), we confirm 35 unique protocluster members with at least two emission lines detected with S/N $>$ 3. Combined with 12 extra members from the zCOSMOS-deep spectroscopic survey (47 in total), we estimate a mean redshift and a line-of-sight velocity dispersion of $z_{mean}$=2.23224 $pm$ 0.00101 and $sigma_{los}$=645 $pm$ 69 km s$^{-1}$ for this protocluster, respectively. Assuming virialization and spherical symmetry for the system, we estimate a total mass of $M_{vir}$ $sim$ $(1-2) times$10$^{14}$ $M_{odot}$ for the structure. We evaluate a number density enhancement of $delta_{g}$ $sim$ 7 for this system and we argue that the structure is likely not fully virialized at $z$ $sim$ 2.2. However, in a spherical collapse model, $delta_{g}$ is expected to grow to a linear matter enhancement of $sim$ 1.9 by $z$=0, exceeding the collapse threshold of 1.69, and leading to a fully collapsed and virialized Coma-type structure with a total mass of $M_{dyn}$($z$=0) $sim$ 9.2$times$10$^{14}$ $M_{odot}$ by now. This observationally efficient confirmation suggests that large narrowband emission-line galaxy surveys, when combined with ancillary photometric data, can be used to effectively trace the large-scale structure and protoclusters at a time when they are mostly dominated by star-forming galaxies.
We present the results of near-infrared spectroscopic observations of the $K$-band selected candidate galaxies in the protocluster at $z=3.09$ in the SSA22 field. We observed 67 candidates with $K_{rm AB}<24$ and confirmed redshifts of the 39 galaxies at $2.0< z_{rm spec}< 3.4$. Of the 67 candidates, 24 are certainly protocluster members with $3.04leq z_{rm spec}leq 3.12$, which are massive red galaxies those have been unidentified in previous optical observations of the SSA22 protocluster. Many distant red galaxies (DRGs; $J-K_{rm AB}>1.4$), hyper extremely red objects (HEROs; $J-K_{rm AB}>2.1$), {it Spitzer} MIPS 24 $mu$m sources, active galactic nuclei (AGNs) as well as the counterparts of Ly$alpha$ blobs and the AzTEC/ASTE 1.1-mm sources in the SSA22 field are also found to be the protocluster members. The mass of the SSA22 protocluster is estimated to be $sim2-5times10^{14}~M_{odot}$ and this system is plausibly a progenitor of the most massive clusters of galaxies in the current Universe. The reddest ($J-K_{rm AB}geq 2.4$) protocluster galaxies are massive galaxies with $M_{rm star}sim10^{11}~M_{odot}$ showing quiescent star formation activities and plausibly dominated by old stellar populations. Most of these massive quiescent galaxies host moderately luminous AGNs detected by X-ray. There are no significant differences in the [O{footnotesize III}] $lambda$5007/H$beta$ emission line ratios, and [O{footnotesize III}] $lambda$5007 line widths and spatial extents of the protocluster galaxies from those of massive galaxies at $zsim2-3$ in the general field.
The aim of this paper is the spectroscopic study of 13 galaxies belonging to the field of the protocluster associated with the radio galaxy (RG) 7C 1756+6520 at z = 1.4156. In particular, we focus on the characterization of the nuclear activity. This analysis has been performed on rest-frame optical spectra taken with LBT-LUCI. The spectral coverage allowed us to observe emission lines such as Halpha, Hbeta, [Oiii]5007 A, and [Nii]6583 A at the z of the central RG. We observed the central part of the protocluster, which is suitable to include the radio galaxy, several spectroscopically confirmed AGN belonging to the protocluster, and other objects that might be members of the protocluster. For four previously identified protocluster members, we derived the redshift by detecting emission lines that have never detected before for these galaxies. The stacked spectrum of the galaxies in which we detected the [Oiii]5007 A emission line revealed the presence of the second line of the [Oiii] doublet at 4959 A and of Hbeta, which confirms that they belong to the protocluster. By collecting all members identified so far in this work and other members from the literature, we defined 31 galaxies, including the central RG, around z = 1.4152 +/- 0.056, corresponding to peculiar velocities <~5000 km/s with respect to the RG. The PV phase-space diagram suggests that 3 protocluster AGN and the central RG might be a virialized population that has been coexisting for a long time in the densest core region of this forming structure. This protocluster is characterized by a high fraction of AGN (23%). For one of them, AGN1317, we produced 2 BPT diagrams. The high fraction of AGN and their distribution within the protocluster seem to be consistent with predictions of some theoretical models on AGN growth and feedback.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
