Abstract
We present stacked average far-infrared spectra of a sample of 197 dusty star-forming galaxies (DSFGs) at
using about 90% of the
Herschel Space Observatory
SPIRE Fourier Transform ...Spectrometer (FTS) extragalactic data archive based on 3.5 years of science operations. These spectra explore an observed-frame 447–1568 GHz frequency range, allowing us to observe the main atomic and molecular lines emitted by gas in the interstellar medium. The sample is subdivided into redshift bins, and a subset of the bins are stacked by infrared luminosity as well. These stacked spectra are used to determine the average gas density and radiation field strength in the photodissociation regions (PDRs) of DSFGs. For the low-redshift sample, we present the average spectral line energy distributions of CO and H
2
O rotational transitions and consider PDR conditions based on observed C
i
370 and 609
μ
m, and CO (7-6) lines. For the high-
z
(
) sample, PDR models suggest a molecular gas distribution in the presence of a radiation field that is at least a factor of 10
3
larger than the Milky Way and with a neutral gas density of roughly
–
cm
−3
. The corresponding PDR models for the low-
z
sample suggest a UV radiation field and gas density comparable to those at high-
z
. Given the challenges in obtaining adequate far-infrared observations, the stacked average spectra we present here will remain the measurements with the highest signal-to-noise ratio for at least a decade and a half until the launch of the next far-infrared facility.
We show that the observed velocity dispersion function of E/S0 galaxies matches strikingly well the distribution function of virial velocities of massive halos virializing at z . 1.5, as predicted by ...the standard hierarchical clustering scenario in a ACDM cosmology, for a constant ratio s/V sub(vir) 0.55 c 0.05, which is close to the value expected at virialization if it typically occurred at z 3. This strongly suggests that dissipative processes and later merging events had little impact on the matter density profile. Adopting the above s/V sub(vir) ratio, the observed relationships between photometric and dynamical properties that define the fundamental plane of elliptical galaxies, such as the luminosity-s (Faber-Jackson) and the luminosity-effective radius relations, as well as the M sub(BH)-s relation, are nicely reproduced. Their shapes turn out to be determined by the mutual feedback of star formation (and supernova explosions) and nuclear activity, along the lines discussed by Granato and coworkers. To our knowledge, this is the first semianalytic model for which simultaneous fits of the fundamental plane relations and of the epoch-dependent luminosity function of spheroidal galaxies have been presented.
Herschel -ATLAS and ALMA Messias, Hugo; Dye, Simon; Nagar, Neil ...
Astronomy and astrophysics (Berlin),
08/2014, Volume:
568
Journal Article
Peer reviewed
Open access
Context. The submillimetre-bright galaxy population is believed to comprise, aside from local galaxies and radio-loud sources, intrinsically active star-forming galaxies, the brightest of which are ...lensed gravitationally. The latter enable studies at a level of detail beyond what is usually possible by the observation facility. Aims: This work focuses on one of these lensed systems, HATLAS J142935.3-002836 (H1429-0028), selected in the Herschel-ATLAS field. Gathering a rich, multi-wavelength dataset, we aim to confirm the lensing hypothesis and model the background source's morphology and dynamics, as well as to provide a full physical characterisation. Methods: Multi-wavelength high-resolution data is utilised to assess the nature of the system. A lensing-analysis algorithm that simultaneously fits different wavebands is adopted to characterise the lens. The background galaxy dynamical information is studied by reconstructing the 3D source plane of the ALMA CO (J:4 → 3) transition. Near-IR imaging from HST and Keck-AO allows to constrain rest-frame optical photometry independently for the foreground and background systems. Physical parameters (such as stellar and dust masses) are estimated via modelling of the spectral energy distribution taking source blending, foreground obscuration, and differential magnification into account. Results: The system comprises a foreground edge-on disk galaxy (at zsp = 0.218) with an almost complete Einstein ring around it. The background source (at zsp = 1.027) is magnified by a factor of μ ~ 8-10 depending on wavelength. It is comprised of two components and a tens-of-kpc-long tidal tail resembling the Antennæ merger. As a whole, the background source is a massive stellar system (1.32-0.41+ 0.63 × 1011 M⊙) forming stars at a rate of 394 ± 90 M⊙ yr-1, and it has a significant gas reservoir MISM = 4.6 ± 1.7 × 1010 M⊙. Its depletion time due to star formation alone is thus expected to be τSF = MISM/ SFR = 117 ± 51 Myr. The dynamical mass of one of the components is estimated to be 5.8 ± 1.7 × 1010 M⊙, and, together with the photometric total mass estimate, it implies that H1429-0028 is a major merger system (1:2.8-1.5+1.8).
ABSTRACT The Australia Telescope 20GHz (AT20G) survey is a blind survey of the whole Southern sky at 20GHz with follow-up observations at 4.8, 8.6 and 20 GHz carried out with the Australia Telescope ...Compact Array (ATCA) from 2004 to 2008. In this paper we present an analysis of radio spectral properties in total intensity and polarization, sizes, optical identifications and redshifts of the sample of the 5808 extragalactic sources in the survey catalogue of confirmed sources over 6.1 sr in the Southern sky (i.e. the whole Southern sky excluding the strip at Galactic latitude |b| < ). The sample has a flux density limit of 40mJy. Completeness has been measured as a function of scan region and flux density. Averaging over the whole survey area the follow-up survey is 78 per cent complete above 50mJy and 93 per cent complete above 100mJy. 3332 sources with declination δ < -15° have good quality almost simultaneous observations at 4.8, 8.6 and 20GHz. The spectral analysis shows that the sample is dominated by flat-spectrum sources, with 69 per cent having spectral index α208.6 > - 0.5 (Sνα). The fraction of flat-spectrum sources decreases from 81 per cent for S20GHz > 500 mJy to 60 per cent for S20GHz < 100 mJy. There is also a clear spectral steepening at higher frequencies with the median α decreasing from -0.16 between 4.8 and 8.6 GHz to -0.28 between 8.6 and 20 GHz. Simultaneous observations in polarization are available for all the sources at all the frequencies. 768 sources have a good-quality detection of polarized flux density at 20 GHz; 467 of them were also detected in polarization at 4.8 and/or at 8.6 GHz so that it has been possible to compare the spectral behaviour in total intensity and polarization. We have found that the polarized fraction increases slightly with frequency and decreases with flux density. The spectral indices in total intensity and in polarization are, on average, close to each other, but we also found several sources for which the spectral shape of the polarized emission is substantially different from the spectral shape in total intensity. The correlation between the spectral indices in total intensity and in polarization is weaker for flat-spectrum sources. Cross-matches and comparisons have been made with other catalogues at lower radio frequencies, and in the optical, X-ray and γ-ray bands. Redshift estimates are available for 825 sources. PUBLICATION ABSTRACT
We present stacked average far-infrared spectra of a sample of 197 dusty star-forming galaxies (DSFGs) at using about 90% of the Herschel Space Observatory SPIRE Fourier Transform Spectrometer (FTS) ...extragalactic data archive based on 3.5 years of science operations. These spectra explore an observed-frame 447-1568 GHz frequency range, allowing us to observe the main atomic and molecular lines emitted by gas in the interstellar medium. The sample is subdivided into redshift bins, and a subset of the bins are stacked by infrared luminosity as well. These stacked spectra are used to determine the average gas density and radiation field strength in the photodissociation regions (PDRs) of DSFGs. For the low-redshift sample, we present the average spectral line energy distributions of CO and H2O rotational transitions and consider PDR conditions based on observed C i 370 and 609 m, and CO (7-6) lines. For the high-z ( ) sample, PDR models suggest a molecular gas distribution in the presence of a radiation field that is at least a factor of 103 larger than the Milky Way and with a neutral gas density of roughly - cm−3. The corresponding PDR models for the low-z sample suggest a UV radiation field and gas density comparable to those at high-z. Given the challenges in obtaining adequate far-infrared observations, the stacked average spectra we present here will remain the measurements with the highest signal-to-noise ratio for at least a decade and a half until the launch of the next far-infrared facility.
The Planck-ATCA Coeval Observations (PACO) project collected data between 4.5 and 40 GHz for 482 sources selected within the Australia Telescope 20 GHz (AT20G) catalogue and observed with the ...Australia Telescope Compact Array. Observations were done almost simultaneously with the Planck satellite, in the period between 2009 July and 2010 August. In this paper, we present and discuss the data for the complete sample of 159 sources with S
AT20G > 200 mJy in the South Ecliptic Pole region.
The Planck Early Release Compact Source Catalogue (ERCSC) contains 57 of our sources. A comparison between the PACO catalogue and the ERCSC confirms that the reliability of the latter is better than 95 per cent. The missing ERCSC sources are typically associated with the Large Magellanic Cloud, the Milky Way or are otherwise extended.
The spectral analysis of the PACO faint catalogue shows a spectral steepening of the sources at high frequencies, confirming the results obtained from the PACO bright sample.
A comparison with AT20G measurements, carried out, on average, a few years earlier, has demonstrated that, on these time-scales, our sources show a rather high variability with an rms amplitude of ≃40 per cent at 20 GHz. The source spectral properties are found not to vary substantially with flux density, except for an increase in the fraction of steep spectrum sources at fainter flux densities.
Our data also allow us to extend by a factor of ≃5 downwards in flux density the source counts at ≃33 and ≃40 GHz obtained from the ERCSC. This allows us to substantially improve our control on the contribution of unresolved extragalactic sources to the power spectrum of small-scale fluctuations in cosmic microwave background maps.
The Australia Telescope 20 GHz (AT20G) survey is a blind survey of the whole Southern sky at 20 GHz with follow-up observations at 4.8, 8.6 and 20 GHz carried out with the Australia Telescope Compact ...Array (ATCA) from 2004 to 2008. In this paper we present an analysis of radio spectral properties in total intensity and polarization, sizes, optical identifications and redshifts of the sample of the 5808 extragalactic sources in the survey catalogue of confirmed sources over 6.1 sr in the Southern sky (i.e. the whole Southern sky excluding the strip at Galactic latitude |b| <
).
The sample has a flux density limit of 40 mJy. Completeness has been measured as a function of scan region and flux density. Averaging over the whole survey area the follow-up survey is 78 per cent complete above 50 mJy and 93 per cent complete above 100 mJy. 3332 sources with declination δ < −15° have good quality almost simultaneous observations at 4.8, 8.6 and 20 GHz. The spectral analysis shows that the sample is dominated by flat-spectrum sources, with 69 per cent having spectral index α20
8.6 > − 0.5 (S∝να). The fraction of flat-spectrum sources decreases from 81 per cent for S
20 GHz > 500 mJy to 60 per cent for S
20 GHz < 100 mJy. There is also a clear spectral steepening at higher frequencies with the median α decreasing from −0.16 between 4.8 and 8.6 GHz to −0.28 between 8.6 and 20 GHz.
Simultaneous observations in polarization are available for all the sources at all the frequencies. 768 sources have a good-quality detection of polarized flux density at 20 GHz; 467 of them were also detected in polarization at 4.8 and/or at 8.6 GHz so that it has been possible to compare the spectral behaviour in total intensity and polarization. We have found that the polarized fraction increases slightly with frequency and decreases with flux density. The spectral indices in total intensity and in polarization are, on average, close to each other, but we also found several sources for which the spectral shape of the polarized emission is substantially different from the spectral shape in total intensity. The correlation between the spectral indices in total intensity and in polarization is weaker for flat-spectrum sources.
Cross-matches and comparisons have been made with other catalogues at lower radio frequencies, and in the optical, X-ray and γ-ray bands. Redshift estimates are available for 825 sources.
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