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Register a new userA Dust-Obscured Massive Maximum-Starburst Galaxy at a Redshift of 6.34
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Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts - that is, increased rates of star formation - in the most massive dark matter halos at early epochs. However, it remains unknown how soon after the Big Bang such massive starburst progenitors exist. The measured redshift distribution of dusty, massive starbursts has long been suspected to be biased low in redshift owing to selection effects, as confirmed by recent findings of systems out to redshift z~5. Here we report the identification of a massive starburst galaxy at redshift 6.34 through a submillimeter color-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40% of the baryonic mass. A maximum starburst converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn of cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang.
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We describe the search for Lyman-break galaxies (LBGs) near the sub-millimeter bright starburst galaxy HFLS3 at $z$$=$6.34 and a study on the environment of this massive galaxy during the end of reionization.We performed two independent selections of LBGs on images obtained with the textit{Gran Telescopio Canarias} (GTC) and the textit{Hubble Space Telescope} (HST) by combining non-detections in bands blueward of the Lyman-break and color selection. A total of 10 objects fulfilling the LBG selection criteria at $z$$>$5.5 were selected over the 4.54 and 55.5 arcmin$^2$ covered by our HST and GTC images, respectively. The photometric redshift, UV luminosity, and the star-formation rate of these sources were estimated with models of their spectral energy distribution. These $z$$sim$6 candidates have physical properties and number densities in agreement with previous results. The UV luminosity function at $z$$sim$6 and a Voronoi tessellation analysis of this field shows no strong evidence for an overdensity of relatively bright objects (m$_{F105W}$$<$25.9) associated with textit{HFLS3}. However, the over-density parameter deduced from this field and the surface density of objects can not excluded definitively the LBG over-density hypothesis. Moreover we identified three faint objects at less than three arcseconds from textit{HFLS3} with color consistent with those expected for $z$$sim$6 galaxies. Deeper data are needed to confirm their redshifts and to study their association with textit{HFLS3} and the galaxy merger that may be responsible for the massive starburst.
Feedback-driven winds from star formation or active galactic nuclei might be a relevant channel for the abrupt quenching star formation in massive galaxies. However, both observations and simulations support the idea that these processes are non-conflictingly co-evolving and self-regulating. Furthermore, evidence of disruptive events that are capable of fast quenching is rare, and constraints on their statistical prevalence are lacking. Here we present a massive starburst galaxy at z=1.4 which is ejecting $46 pm 13$% of its molecular gas mass at a startling rate of $gtrsim 10,000$ M$_{odot}{rm yr}^{-1}$. A broad component that is red-shifted from the galaxy emission is detected in four (low- and high-J) CO and [CI] transitions and in the ionized phase, which ensures a robust estimate of the expelled gas mass. The implied statistics suggest that similar events are potentially a major star-formation quenching channel. However, our observations provide compelling evidence that this is not a feedback-driven wind, but rather material from a merger that has been probably tidally ejected. This finding challenges some literature studies in which the role of feedback-driven winds might be overstated.
We present ALMA observations and multiwavelength spectral energy distribution (SED) analysis in a WISE-selected, hyperluminous dust-obscured quasar W0533-3401 at $z=2.9$. We derive its physical properties of each component, such as molecular gas, stars, dust and the central supermassive black hole (SMBH). Both the dust continuum at 3 mm and the CO(3-2) line are detected. The derived molecular gas mass $M_{rm gas}=8.4times10^{10} M_odot$ and its fraction $f_{rm gas}=0.7$ suggest that W0533-3401 is gas-rich. The star formation rate (SFR) has been estimated to be $sim3000-7000 M_odot$ yr$^{-1}$ by using different methods. The high values of SFR and specific SFR suggest that W0533-3401 is a maximum-starburst. The corresponding gas depletion timescales are very short ($t_{rm depl}sim12-28$ Myr). The CO(3-2) emission line is marginally resolved and has a velocity gradient, which is possibly due to a rotating gas disk, gas outflow or merger. Finally, we infer the black hole mass growth rate of W0533-3401 (${dot{M}}_{rm BH}$ = 49 $M_odot$ yr$^{-1}$), which suggests a rapid growth of the central SMBH. The observed black hole to stellar mass ratio $M_{rm BH}/M_star$ of W0533-3401, which is dependent on the adopted Eddington ratio, is over one order of magnitude higher than the local value, and is evolving towards the evolutionary trend of unobscured quasars. Our results are consistent with the scenario that wobs, with both a gas-rich maximum-starburst and a rapid black hole growth, is experiencing a short transition phase towards an unobscured quasar.
Star-formation in the galaxy populations of local massive clusters is reduced with respect to field galaxies, and tends to be suppressed in the core region. Indications of a reversal of the star-formation--density relation have been observed in a few z >1.4 clusters. Using deep imaging from 100-500um from PACS and SPIRE onboard Herschel, we investigate the infrared properties of spectroscopic and photo-z cluster members, and of Halpha emitters in XMMU J2235.3-2557, one of the most massive, distant, X-ray selected clusters known. Our analysis is based mostly on fitting of the galaxies spectral energy distribution in the rest-frame 8-1000um. We measure total IR luminosity, deriving star formation rates (SFRs) ranging from 89-463 Msun/yr for 13 galaxies individually detected by Herschel, all located beyond the core region (r >250 kpc). We perform a stacking analysis of nine star-forming members not detected by PACS, yielding a detection with SFR=48 Msun/yr. Using a color criterion based on a star-forming galaxy SED at the cluster redshift we select 41 PACS sources as candidate star-forming cluster members. We characterize a population of highly obscured SF galaxies in the outskirts of XMMU J2235.3-2557. We do not find evidence for a reversal of the SF-density relation in this massive, distant cluster.
Based on broad/narrow-band photometry and Keck DEIMOS spectroscopy we report a redshift of z=4.64-0.08+0.06 for AzTEC/COSMOS 1, the brightest sub-mm galaxy in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 micron), CSO/SHARC II (350 micron), CARMA and PdBI (3 mm). We do not detect CO(5-4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3sigma upper limits on the gas mass to <~8x10^9 M_Sol and <~5x10^10 M_Sol, respectively (assuming similar conditions as observed in z~2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (<~50 Myr), massive (M*~10^11 M_Sol), but compact (<~2 kpc) galaxy forming stars at a rate of ~1300 M_Sol/yr. Our results imply that AzTEC 1 is forming stars in a gravitationally bound regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.
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