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Register a new userWhich halos host Herschel-ATLAS galaxies in the local Universe?
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We measure the projected cross-correlation between low redshift (z < 0.5) far-IR selected galaxies in the SDP field of the Herschel-ATLAS (H-ATLAS) survey and optically selected galaxies from the Galaxy and Mass Assembly (GAMA) redshift survey. In order to obtain robust correlation functions, we restrict the analysis to a subset of 969 out of 6900 H-ATLAS galaxies, which have reliable optical counterparts with r<19.4 mag and well-determined spectroscopic redshifts. The overlap region between the two surveys is 12.6 sq. deg; the matched sample has a median redshift of z ~ 0.2. The cross-correlation of GAMA and H-ATLAS galaxies within this region can be fitted by a power law, with correlation length r_0 ~ 4.63 +/- 0.51 Mpc. Comparing with the corresponding auto-correlation function of GAMA galaxies within the SDP field yields a relative bias (averaged over 2-8 Mpc) of H-ATLAS and GAMA galaxies of b_H/b_G ~ 0.6. Combined with clustering measurements from previous optical studies, this indicates that most of the low redshift H-ATLAS sources are hosted by halos with masses comparable to that of the Milky Way. The correlation function appears to depend on the 250 um luminosity, L_250, with bright (median luminosity u L_250 ~ 1.6 x 10^10 L_sun) objects being somewhat more strongly clustered than faint ( u L_250 ~ 4.0 x 10^9 L_sun) objects. This implies that galaxies with higher dust-obscured star formation rates are hosted by more massive halos.
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We present the properties of the first 250 $mu$m blind sample of nearby galaxies (15 < D < 46 Mpc) containing 42 objects from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). Herschels sensitivity probes the faint end of the dust luminosity function for the first time, spanning a range of stellar mass (7.4 < log$_{10}$ M$_{star}$ < 11.3 M$_{odot}$), star formation activity (-11.8 < log$_{10}$ SSFR < -8.9 yr$^{-1}$), gas fraction (3-96 per cent), and colour (0.6 < FUV-Ks < 7.0 mag). The median cold dust temperature is 14.6 K, colder than in the Herschel Reference Survey (18.5 K) and Planck Early Release Compact Source Catalogue 17.7 K. The mean dust-to-stellar mass ratio in our sample is higher than these surveys by factors of 3.7 and 1.8, with a dust mass volume density of (3.7 $pm$ 0.7) x 10$^{5}$ M$_{odot}$ Mpc$^{-3}$. Counter-intuitively, we find that the more dust rich a galaxy, the lower its UV attenuation. Over half of our dust-selected sample are very blue in FUV-Ks colour, with irregular and/or highly flocculent morphology, these galaxies account for only 6 per cent of the samples stellar mass but contain over 35 per cent of the dust mass. They are the most actively star forming galaxies in the sample, with the highest gas fractions and lowest UV attenuation. They also appear to be in an early stage of converting their gas into stars, providing valuable insights into the chemical evolution of young galaxies.
We present an analysis of CO molecular gas tracers in a sample of 500{mu}m-selected Herschel-ATLAS galaxies at z<0.05 (cz<14990km/s). Using 22-500{mu}m photometry from WISE, IRAS and Herschel, with HI data from the literature, we investigate correlations between warm and cold dust, and tracers of the gas in different phases. The correlation between global CO(3-2) line fluxes and FIR-submillimetre fluxes weakens with increasing IR wavelength ({lambda}>60{mu}m), as a result of colder dust being less strongly associated with dense gas. Conversely, CO(2-1) and HI line fluxes both appear to be better correlated with longer wavelengths, suggesting that cold dust is more strongly associated with diffuse atomic and molecular gas phases, consistent with it being at least partially heated by radiation from old stellar populations. The increased scatter at long wavelengths implies that submillimetre fluxes are a poorer tracer of SFR. Fluxes at 22 and 60{mu}m are also better correlated with diffuse gas tracers than dense CO(3-2), probably due to very-small-grain emission in the diffuse interstellar medium, which is not correlated with SFR. The FIR/CO luminosity ratio and the dust mass/CO luminosity ratio both decrease with increasing luminosity, as a result of either correlations between mass and metallicity (changing CO/H2) or between CO luminosity and excitation [changing CO(3-2)/CO(1-0)].
The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 510 square degrees of the extragalactic sky, four times larger than all the other Herschel surveys combined, in five far-infrared and submillimetre bands. We describe the survey, the complementary multi-wavelength datasets that will be combined with the Herschel data, and the six major science programmes we are undertaking. Using new models based on a previous submillimetre survey of galaxies, we present predictions of the properties of the ATLAS sources in other wavebands.
We study the contribution of galaxies with different properties to the global densities of star formation rate (SFR), atomic (HI) and molecular hydrogen (H2) as a function of redshift. We use the GALFORM model of galaxy formation, which is set in the LCDM framework. This model includes a self-consistent calculation of the SFR, which depends on the H2 content of galaxies. The predicted SFR density and how much of this is contributed by galaxies with different stellar masses and infrared luminosities are in agreement with observations. The model predicts a modest evolution of the HI density at z<3, which is also in agreement with the observations. The HI density is predicted to be always dominated by galaxies with SFR<1Msun/yr. This contrasts with the H2 density, which is predicted to be dominated by galaxies with SFR>10Msun/yr. Current high-redshift galaxy surveys are limited to detect carbon monoxide in galaxies with SFR>30Msun/yr, which in our model make up, at most, 20% of the H2 in the universe. In terms of stellar mass, the predicted H2 density is dominated by massive galaxies, Mstellar>10^10Msun, while the HI density is dominated by low mass galaxies, Mstellar<10^9Msun. In the context of upcoming neutral gas surveys, we suggest that the faint nature of the galaxies dominating the HI content of the Universe will hamper the identification of optical counterparts, while for H2, we expect follow up observations of molecular emission lines of already existing galaxy catalogues to be able to uncover the H2 density of the Universe.
We investigate the host galaxies of compact objects merging in the local Universe, by combining the results of binary population-synthesis simulations with the Illustris cosmological box. Double neutron stars (DNSs) merging in the local Universe tend to form in massive galaxies (with stellar mass $>10^{9}$ M$_odot$) and to merge in the same galaxy where they formed, with a short delay time between the formation of the progenitor stars and the DNS merger. In contrast, double black holes (DBHs) and black hole $-$ neutron star binaries (BHNSs) form preferentially in small galaxies (with stellar mass $<10^{10}$ M$_odot$) and merge either in small or in larger galaxies, with a long delay time. This result is an effect of metallicity: merging DBHs and BHNSs form preferentially from metal-poor progenitors ($Zleq{}0.1$ Z$_odot$), which are more common in high-redshift galaxies and in local dwarf galaxies, whereas merging DNSs are only mildly sensitive to progenitors metallicity and thus are more abundant in massive galaxies nowadays. The mass range of DNS hosts we predict in this work is consistent with the mass range of short gamma-ray burst hosts.
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