We report the spectroscopic confirmation of a submillimeter galaxy (SMG) at s = 4.547 with an estimated L sub(IR) = (0.5-2.0) x 10 super(13) L. The spectra, mid-IR, and X-ray properties indicate the ...bolometric luminosity is dominated by star formation at a rate of >1000 M Yr super(-1). Multiple, spatially separated components are visible in the Lya line with an observed velocity difference of up to 380 km s super(-1) and the object morphology indicates a merger. The best-fit spectral energy distribution and spectral line indicators suggest the object is 2-8 Myr old and contains >10 super(10) M of stellar mass. This object is a likely progenitor for the massive early-type systems seen at z similar to 2.
We present first results of a study aimed to constrain the star formation rate and dust content of galaxies at z~2. We use a sample of BzK-selected star-forming galaxies, drawn from the COSMOS ...survey, to perform a stacking analysis of their 1.4 GHz radio continuum as a function of different stellar population properties, after removing AGN contaminants from the sample. Dust unbiased star formation rates are derived from radio fluxes assuming the local radio-IR correlation. The main results of this work are: i) specific star formation rates are constant over about 1 dex in stellar mass and up to the highest stellar mass probed; ii) the dust attenuation is a strong function of galaxy stellar mass with more massive galaxies being more obscured than lower mass objects; iii) a single value of the UV extinction applied to all galaxies would lead to grossly underestimate the SFR in massive galaxies; iv) correcting the observed UV luminosities for dust attenuation based on the Calzetti recipe provide results in very good agreement with the radio derived ones; v) the mean specific star formation rate of our sample steadily decreases by a factor of ~4 with decreasing redshift from z=2.3 to 1.4 and a factor of ~40 down the local Universe. These empirical SFRs would cause galaxies to dramatically overgrow in mass if maintained all the way to low redshifts, we suggest that this does not happen because star formation is progressively quenched, likely starting from the most massive galaxies.
Most of the baryons in galaxy clusters reside between the galaxies in a hot, tenuous gas. The densest gas in their centres should cool and accrete onto giant central galaxies at rates of 10-1,000 ...solar masses per year. No viable repository for this gas, such as clouds or new stars, has been found. New X-ray observations, however, have revealed far less cooling below X-ray temperatures than expected, altering the previously accepted picture of cooling flows. As a result, most of the gas must be heated to and maintained at temperatures above ∼2 keV (ref. 3). The most promising heating mechanism is powerful radio jets emanating from supermassive black holes in the central galaxies of clusters. Here we report the discovery of giant cavities and shock fronts in a distant (z = 0.22) cluster caused by an interaction between a radio source and the hot gas surrounding it. The energy involved is ∼6 × 1061 erg, the most powerful radio outburst known. This is enough energy to quench a cooling flow for several Gyr, and to provide ∼1/3 keV per particle of heat to the surrounding cluster.
In the low-redshift Universe, the most powerful radio sources are often associated with gas-rich galaxy mergers or interactions. We here present evidence for an advanced, gas-rich (‘wet’) merger ...associated with a powerful radio galaxy at a redshift of z ∼ 2. This radio galaxy, MRC 0152-209, is the most infrared-luminous high-redshift radio galaxy known in the Southern hemisphere. Using the Australia Telescope Compact Array, we obtained high-resolution CO(1–0) data of cold molecular gas, which we complement with Hubble Space Telescope (HST)/Wide Field Planetary Camera 2 (WFPC2) imaging and William Herschel Telescope long-slit spectroscopy. We find that, while roughly M
H2 ∼ 2 × 1010 M⊙ of molecular gas coincides with the central host galaxy, another M
H2 ∼ 3 × 1010 M⊙ is spread across a total extent of ∼60 kpc. Most of this widespread CO(1–0) appears to follow prominent tidal features visible in the rest-frame near-UV HST/WFPC2 imaging. Lyα emission shows an excess over He II, but a deficiency over L
IR, which is likely the result of photoionization by enhanced but very obscured star formation that was triggered by the merger. In terms of feedback, the radio source is aligned with widespread CO(1–0) emission, which suggests that there is a physical link between the propagating radio jets and the presence of cold molecular gas on scales of the galaxy's halo. Its optical appearance, combined with the transformational stage at which we witness the evolution of MRC 0152-209, leads us to adopt the name ‘Dragonfly Galaxy’.
ABSTRACT We present CO(1-0) observations obtained at the Karl G. Jansky Very Large Array for 14 galaxies with existing CO(3-2) measurements, including 11 galaxies that contain active galactic nuclei ...(AGNs) and three submillimeter galaxies (SMGs). We combine this sample with an additional 15 galaxies from the literature that have both CO(1-0) and CO(3-2) measurements in order to evaluate differences in CO excitation between SMGs and AGN host galaxies, to measure the effects of CO excitation on the derived molecular gas properties of these populations, and to look for correlations between the molecular gas excitation and other physical parameters. With our expanded sample of CO(3-2)/CO(1-0) line ratio measurements, we do not find a statistically significant difference in the mean line ratio between SMGs and AGN host galaxies as can be found in the literature; we instead find for AGN host galaxies and for SMGs (or for both populations combined). We also do not measure a statistically significant difference between the distributions of the line ratios for these populations at the p = 0.05 level, although this result is less robust. We find no excitation dependence on the index or offset of the integrated Schmidt-Kennicutt relation for the two CO lines, and we obtain indices consistent with N = 1 for the various subpopulations. However, including low-z "normal" galaxies increases our best-fit Schmidt-Kennicutt index to . While we do not reproduce correlations between the CO line width and luminosity, we do reproduce correlations between CO excitation and star-formation efficiency.
The high-redshift radio galaxy MRC 1138−262 ('Spiderweb Galaxy'; z = 2.16) is one of the most massive systems in the early Universe and surrounded by a dense 'web' of proto-cluster galaxies. Using ...the Australia Telescope Compact Array, we detected CO(1-0) emission from cold molecular gas - the raw ingredient for star formation - across the Spiderweb Galaxy. We infer a molecular gas mass of M
H2 = 6 × 1010 M (for M
H2/L′CO = 0.8). While the bulk of the molecular gas coincides with the central radio galaxy, there are indications that a substantial fraction of this gas is associated with satellite galaxies or spread across the intergalactic medium on scales of tens of kpc. In addition, we tentatively detect CO(1-0) in the star-forming proto-cluster galaxy HAE 229, 250 kpc to the West. Our observations are consistent with the fact that the Spiderweb Galaxy is building up its stellar mass through a massive burst of widespread star formation. At maximum star formation efficiency, the molecular gas will be able to sustain the current star formation rate (SFR 1400 M yr−1, as traced by Seymour et al.) for about 40 Myr. This is similar to the estimated typical lifetime of a major starburst event in infrared luminous merger systems.
We present a CO(1-0) survey for cold molecular gas in a representative sample of 13 high-z radio galaxies (HzRGs) at 1.4 < z < 2.8, using the Australia Telescope Compact Array. We detect CO(1-0) ...emission associated with five sources: MRC 0114-211, MRC 0152-209, MRC 0156-252, MRC 1138-262 and MRC 2048-272. The CO(1-0) luminosities are in the range
K km s−1 pc2. For MRC 0152-209 and MRC 1138-262, part of the CO(1-0) emission coincides with the radio galaxy, while part is spread on scales of tens of kpc and likely associated with galaxy mergers. The molecular gas mass derived for these two systems is M
H2 ∼ 6 × 1010 M (M
H2/
= 0.8). For the remaining three CO-detected sources, the CO(1-0) emission is located in the halo (∼50-kpc) environment. These three HzRGs are among the fainter far-IR emitters in our sample, suggesting that similar reservoirs of cold molecular halo gas may have been missed in earlier studies due to pre-selection of IR-bright sources. In all three cases, the CO(1-0) is aligned along the radio axis and found beyond the brightest radio hotspot, in a region devoid of 4.5 μm emission in Spitzer imaging. The CO(1-0) profiles are broad, with velocity widths of ∼1000-3600 km s−1. We discuss several possible scenarios to explain these halo reservoirs of CO(1-0). Following these results, we complement our CO(1-0) study with detections of extended CO from the literature and find at marginal statistical significance (95 per cent level) that CO in HzRGs is preferentially aligned towards the radio jet axis. For the eight sources in which we do not detect CO(1-0), we set realistic upper limits of
K km s−1 pc2. Our survey reveals a CO(1-0) detection rate of 38 per cent, allowing us to compare the CO(1-0) content of HzRGs with that of other types of high-z galaxies.
ABSTRACT We present direct estimates of the mean sky brightness temperature in observing bands around 99 and 242 GHz due to line emission from distant galaxies. These values are calculated from the ...summed line emission observed in a blind, deep survey for spectral line emission from high redshift galaxies using ALMA (the ALMA spectral deep field observations "ASPECS" survey). In the 99 GHz band, the mean brightness will be dominated by rotational transitions of CO from intermediate and high redshift galaxies. In the 242 GHz band, the emission could be a combination of higher order CO lines, and possibly C ii 158 m line emission from very high redshift galaxies (z ∼ 6-7). The mean line surface brightness is a quantity that is relevant to measurements of spectral distortions of the cosmic microwave background, and as a potential tool for studying large-scale structures in the early universe using intensity mapping. While the cosmic volume and the number of detections are admittedly small, this pilot survey provides a direct measure of the mean line surface brightness, independent of conversion factors, excitation, or other galaxy formation model assumptions. The mean surface brightness in the 99 GHZ band is: TB = 0.94 0.09 K. In the 242 GHz band, the mean brightness is: TB = 0.55 0.033 K. These should be interpreted as lower limits on the average sky signal, since we only include lines detected individually in the blind survey, while in a low resolution intensity mapping experiment, there will also be the summed contribution from lower luminosity galaxies that cannot be detected individually in the current blind survey.
We present an analysis of the starburst in the Abell 1835 cluster's cD galaxy. The dense gas surrounding the galaxy is radiating X-rays at a rate of 610 super(45) ergs s super(-1), which is ...consistent with a cooling rate of 6 1000-2000 Mz yr super(-1). However, Chandra and XMM-Newton observations found less than 200 Mz yr super(-1) of cooling below 62 keV, a level that is consistent with the cD's current star formation rate of 100-180 Mz yr super(-1). One or more heating agents (feedback) must then be replenishing the remaining radiative losses. Supernova explosions and thermal conduction are unable to do so. However, the active galactic nucleus (AGN) is pumping 1.4 x 10 super(45) ergs s super(-1) into the hot gas, which is enough power to offset most of the radiative cooling losses. The AGN jet power exceeds the radio synchrotron power by 64000 times, making this one of the most radiatively inefficient radio sources known. The jet power implies that the supermassive black hole has accreted at a mean rate of 60.3 Mz yr super(-1) over the last 40 Myr or so, which is a small fraction of the Eddington accretion rate for a 610 super(9) Mz black hole. The ratio of black hole growth rate by accretion to bulge growth by star formation is consistent with the slope of the (Magorrian) relationship between bulge and central black hole mass in nearby quiescent galaxies. The starburst follows the Schmidt-Kennicutt parameterizations, indicating that the local environment is not substantially altering the IMF and other conditions leading to the onset of star formation. The consistency between net cooling, heating (feedback), and the cooling sink (star formation) in this system resolves the primary objection to traditional cooling flow models.
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