93 research outputs found
Submillimetre Cosmology at High Angular Resolution
Over the last decade observations at submillimetre (submm) and millimetre
(mm) wavelengths, with their unique ability to trace molecular gas and dust,
have attained a central role in our exploration of galaxies at all redshifts.
Due to the limited sensitivities and angular resolutions of current submm/mm
telescopes, however, only the most luminous objects have been uncovered at high
redshifts, with interferometric follow-up observations succeeding in resolving
the dust and gas reservoirs in only a handful of cases. The coming years will
witness a drastic improvement in the current situation, thanks to the arrival
of a new suite of powerful submm observatories (single-dish and
interferometers) with an order of magnitude improvement in sensitivity and
resolution. In this overview I outline a few of what I expect to be the major
advances in the field of galaxy formation and evolution that these new
ground-breaking facilities will facilitate.Comment: (10 pages, 3 figures. Invited talk, proceedings for the 3rd ARENA
Conference "An astronomical observatory at CONCORDIA (Antarctica) for the
next decade", 11-15 May 2009, Frascati, Ital
A 1200-micron MAMBO survey of ELAISN2 and the Lockman Hole - I. Maps, sources and number counts
The definitive version is available at www.blackwell-synergy.com '.--Copyright Blackwell Publishing. DOI : 10.1111/j.1365-2966.2004.08235.xWe present a deep, new 1200μm survey of the ELAISN2 and Lockman Hole fields using the Max Planck Millimeter Bolometer array (MAMBO). The areas surveyed are 160 arcmin2 in ELAISN2 and 197 arcmin2 in the Lockman Hole, covering the entire SCUBA ‘8mJy Survey’. In total, 27 (44) sources have been detected at a significance 4.0 ( 3.5 ). The primary goals of the survey were to investigate the reliability of (sub)millimetre galaxy (SMG) samples, to analyse SMGs using flux ratios sensitive to redshift at z > 3, and to search for ‘SCUBA drop-outs’, i.e. galaxies at z >> 3. We present the 1200μm number counts and find evidence of a fall at bright flux levels. Employing parametric models for the evolution of the local 60μm IRAS luminosity function (LF), we are able to account simultaneously for the 1200 and 850μm counts, suggesting that the MAMBO and SCUBA sources trace the same underlying population of high-redshift, dust-enshrouded galaxies. From a nearest-neighbour clustering analysis we find tentative evidence that themost significantMAMBO sources come in pairs, typically separated by 23′′. Our MAMBO observations unambiguously confirm around half of the SCUBA sources. In a robust sub-sample of 13 SMGs detected by both MAMBO and SCUBA at a significance 3.5 , only one has no radio counterpart. Furthermore, the distribution of 850/1200μmflux density ratios for this sub-sample is consistent with the spectroscopic redshift distribution of radio-detected SMGs (Chapman et al. 2003). Finally, we have searched for evidence of a high-redshift tail of SMGs amongst the 18 MAMBO sources which are not detected by SCUBA. While we cannot rule out that some of them are SCUBA drop-outs at z >> 3, their overall 850-to-1200μm flux distribution is statistically indistinguishable from that of the 13 SMGS which were robustly identified by both MAMBO and SCUBA.Peer reviewe
Interferometric imaging of the high-redshift radio galaxy, 4C60.07: An SMA, Spitzer and VLA study reveals a binary AGN/starburst
‘The definitive version is available at www3.interscience.wiley.com '. Copyright Blackwell / RAS. DOI: 10.1111/j.1365-2966.2008.13811.xPeer reviewe
Tracing Molecular Gas Mass in z ≃ 6 Galaxies with [C ii]
We investigate the fine-structure [C] line at
m as a molecular gas tracer by analyzing the relationship between
molecular gas mass () and [C] line
luminosity () in 11,125 star-forming, main sequence
galaxies from the SIMBA simulations, with line emission modeled by S\'IGAME.
Though most () of the gas mass in our simulations is ionized,
the bulk () of the [C] emission comes from the
molecular phase. We find a sub-linear (slope ) relation, in contrast with the linear relation derived
from observational samples of more massive, metal-rich galaxies at . We derive a median [C]-to- conversion
factor of .
This is lower than the average value of derived from observations, which we attribute to lower gas-phase
metallicities in our simulations. Thus, a lower, luminosity-dependent,
conversion factor must be applied when inferring molecular gas masses from
[C] observations of low-mass galaxies. For our
simulations, [C] is a better tracer of the molecular gas
than CO , especially at the lowest metallicities, where much of the gas
is 'CO-dark'. We find that is more tightly correlated with
than with star-formation rate (), and both the and
relations arise from the Kennicutt-Schmidt relation. Our findings suggest that
is a promising tracer of the molecular gas at the earliest
cosmic epochs.Comment: 13 pages, 9 figures. Accepted for publication in Ap
The SCUBA Half Degree Extragalactic Survey (SHADES) - III : Identification of radio and mid-infrared counterparts to submillimetre galaxies
Peer reviewe
The Herschel view of the environment of the radio galaxy 4C+41.17 at z = 3.8
We present Herschel observations at 70, 160, 250, 350 and 500 μm of the environment of the radio galaxy 4C+41.17 at z = 3.792. About 65 per cent of the extracted sources are securely identified with mid-infrared sources observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 μm. We derive simple photometric redshifts, also including existing 850 and 1200 μm data, using templates of active galactic nuclei, starburst-dominated systems and evolved stellar populations. We find that most of the Herschel sources are foreground to the radio galaxy and therefore do not belong to a structure associated with 4C+41.17. We do, however, find that the spectral energy distribution (SED) of the closest (∼25 arcsec offset) source to the radio galaxy is fully consistent with being at the same redshift as 4C+41.17. We show that finding such a bright source that close to the radio galaxy at the same redshift is a very unlikely event, making the environment of 4C+41.17 a special case. We demonstrate that multiwavelength data, in particular on the Rayleigh–Jeans side of the SED, allow us to confirm or rule out the presence of protocluster candidates that were previously selected by single wavelength data setsPeer reviewe
PRUSSIC. I. A JVLA survey of HCN, HCO+, and HNC (1-0) emission in z ~ 3 dusty galaxiesLow dense-gas fractions in high-redshift star-forming galaxies: low dense-gas fractions in high-redshift star-forming galaxies
GalaxiesInterstellar matter and star formatio
Resolving the ISM at the Peak of Cosmic Star Formation with ALMA: The Distribution of CO and Dust Continuum in z ∼ 2.5 Submillimeter Galaxies
We use Atacama Large Millimeter Array (ALMA) observations of four submillimeter galaxies (SMGs) at z ~ 2–3 to investigate the spatially resolved properties of the interstellar medium (ISM) at scales of 1–5 kpc (0farcs1–0farcs6). The velocity fields of our sources, traced by the 12CO(J = 3–2) emission, are consistent with disk rotation to the first order, implying average dynamical masses of ~3 × 1011 within two half-light radii. Through a Bayesian approach we investigate the uncertainties inherent to dynamically constraining total gas masses. We explore the covariance between the stellar mass-to-light ratio and CO-to-H2 conversion factor, α CO, finding values of for dark matter fractions of 15%. We show that the resolved spatial distribution of the gas and dust continuum can be uncorrelated to the stellar emission, challenging energy balance assumptions in global SED fitting. Through a stacking analysis of the resolved radial profiles of the CO(3–2), stellar, and dust continuum emission in SMG samples, we find that the cool molecular gas emission in these sources (radii ~5–14 kpc) is clearly more extended than the rest-frame ~250 μm dust continuum by a factor >2. We propose that assuming a constant dust-to-gas ratio, this apparent difference in sizes can be explained by temperature and optical depth gradients alone. Our results suggest that caution must be exercised when extrapolating morphological properties of dust continuum observations to conclusions about the molecular gas phase of the interstellar medium (ISM)
CO(1-0) survey of high-z radio galaxies: alignment of molecular halo gas with distant radio sources
We present a CO(1–0) survey for cold molecular gas in a representative sample of 13 highz
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 L
CO ∼ (5–9) × 1010 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 MH2 ∼ 6 × 1010 M� (MH2/L
CO = 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 Spitzerimaging. 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 L
CO ∼ 3–4 × 1010 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
An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field-South: detection of [C II] at z = 4.4
We present Atacama Large Millimeter Array (ALMA) 870-μm (345-GHz) observations of two submillimetre galaxies (SMGs) drawn from an ALMA study of the 126 submillimetre sources from the LABOCA Extended Chandra Deep Field-South Survey (LESS). The ALMA data identify the counterparts to these previously unidentified submillimetre sources and serendipitously detect bright emission lines in their spectra which we show are most likely to be [CII] 157.74 μm emission yielding redshifts of z = 4.42 and 4.44. This blind detection rate within the 7.5-GHz bandpass of ALMA is consistent with the previously derived photometric redshift distribution of SMGs and suggests a modest, but not dominant (≲25 per cent), tail of 870-μm selected SMGs at z ≳ 4. We find that the ratio of L[C II]/LFIR in these SMGs is much higher than seen for similarly far-infrared-luminous galaxies at z ˜ 0, which is attributed to the more extended gas reservoirs in these high-redshift ultraluminous infrared galaxies (ULIRGs). Indeed, in one system we show that the [C II] emission shows hints of extended emission on ≳ 3 kpc scales. Finally, we use the volume probed by our ALMA survey to show that the bright end of the [C II] luminosity function evolves strongly between z = 0 and ˜4.4, reflecting the increased interstellar medium cooling in galaxies as a result of their higher star formation rates. These observations demonstrate that even with short integrations, ALMA is able to detect the dominant fine-structure cooling lines from high-redshift ULIRGs, measure their energetics and spatially resolved properties and trace their evolution with redshift
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