Dust and gas in star-forming galaxies at z ~ 3

Abstract

We present millimetre dust emission measurements of two Lyman Break Galaxies at z ∼ 3 and construct for the first time fully sampled infrared spectral energy distributions (SEDs), from mid-IR to the Rayleigh-Jeans tail, of individually detected, unlensed, UV-selected, main sequence (MS) galaxies at z = 3. The SED modelling of the two sources confirms previous findings, based on stacked ensembles, of an increasing mean radiation field U with redshift, consistent with a rapidly decreasing gas metallicity in z > 2 galaxies. Complementing our study with CO[J=3→2] emission line observations, we measure the molecular gas mass reservoir (M H 2 ) of the systems using three independent approaches: 1) CO line observations, 2) the dust to gas mass ratio vs metallicity relation and 3) a single band, dust emission flux on the Rayleigh-Jeans side of the SED. All techniques return consistent M H 2 estimates within a factor of ∼2 or less, yielding gas depletion time-scales (τ dep ≈ 0.35 Gyrs) and gas-to-stellar mass ratios (M H 2 /M * ≈ 0.5 − 1) for our z ∼ 3 massive MS galaxies. The overall properties of our galaxies are consistent with trends and relations established at lower redshifts, extending the apparent uniformity of star forming-galaxies over the last 11.5 billion years.

Molecular gas content in obscured AGN at z > 1

“…This trend has been confirmed up to z 3; at higher redshifts, CO observations of normal MS galaxies are still scarce (e.g. DessaugesZavadsky et al 2017;Magdis et al 2017), and the SFE evolution is hence primarily constrained by continuum-based gas mass estimates (e.g. Schinnerer et al 2016) which suggest merely slow evolution also beyond z ∼ 3.…”

Starburst to Quiescent from HST/ALMA: Stars and Dust Unveil Minor Mergers in Submillimeter Galaxies at z ∼ 4.5

“…The procedure is as follows. The FIR SED is modeled using the Draine & Li (2007) dust model (DL07; e.g., Magdis et al 2012Magdis et al , 2017Berta et al 2016), L IR is calculated by integrating the best fit to the SED in the range 8-1000 μm, and the SFR IR is obtained using the L IR -to-SFR IR conversion from Kennicutt (1998) for a Chabrier IMF. The SFR UV was calculated employing the Salim et al (2007) prescription that relates L UV to SFR UV for a Chabrier IMF.…”

“…Dust masses are a free parameter in the DL07 model employed, controlling the normalization of the SED. In terms of the dust opacity, DL07 assumes optically thin dust (τ<<1) at all wavelengths (e.g., Magdis et al 2012Magdis et al , 2017Berta et al 2016). Very high dust masses combined with the small sizes derived for the dust-emitting regions implies very high dust mass surface densities (Σ dust = 0.5M dust /πr e,circ 2 ) with values in the range Σ dust = 0.33-5.8 × 10 9 M e kpc −2 (see Table 4) and, consequently, very high extinction.…”

The Strong Gravitationally Lensed Herschel Galaxy HLock01: Optical Spectroscopy Reveals a Close Galaxy Merger with Evidence of Inflowing Gas

“…However, the small rest-frame UV spectral slope of HLock01-B, β=−1.9±0.1 (measured from the observed R and I bands, and assuming a simple power law F λ =λ β ), and the low Balmer/4000 Å break color (F110W-K s =0.15 mag), suggest that the contribution of the LBG in the mid-IR is modest compared with the emission from the SMG. Also, typical LBGs are faint in the mid-IR (S 24 μm ;20-30 μJy; Magdis et al 2010a;Reddy et al 2012), even those showing a redder UV β slope (Reddy et al 2006(Reddy et al , 2010Coppin et al 2007;Siana et al 2008Siana et al , 2009Magdis et al 2017), which are on average more massive and show larger infrared luminosities.…”