GMASS ultradeep spectroscopy of galaxies at z ~ 2

Abstract

Aims. The properties of dust attenuation at rest-frame UV wavelengths are inferred from very high-quality FORS 2 spectra of 78 galaxies from the GMASS survey at redshift 1 < z < 2.5. These objects complement a previously investigated sample of 108 UV-luminous, intermediate-mass (i.e., with stellar masses ∼10 10 −10 11 M ) galaxies at similar redshifts, selected from the FDF spectroscopic survey, the K20 survey, and the GDDS. Detection of the broad absorption feature centred on about 2175 Å ("UV bump") implies that the average UV extinction curve of a galaxy more closely resembles that of the Milky Way (MW) or the Large Magellanic Cloud (LMC), and differs from that of the Small Magellanic Cloud (SMC). Methods. The shape of the UV extinction curve is constrained by a parametric description of the rest-frame UV continuum with the support of a suite of models combining radiative transfer and stellar population synthesis. The UV bump is further characterised by fitting Lorentzian-like profiles. Results. Spectra exhibit a significant 2175 Å feature in at least 30% of the cases, especially those suffering from substantial reddening. If attenuation is dominated by dust ejected from the galaxy main body via galactic winds or more localised superwinds, UV extinction curves in-between those of the SMC and LMC characterise UV-luminous, intermediate-mass galaxies at 1 < z < 2.5. The fraction of galaxies with extinction curves differing from the SMC one increases, if more dust resides in the galactic plane or dust attenuation depends on stellar age. On average, the width of the manifested UV bumps is about 60% of the values typically measured along sightlines in the LMC and MW. This suggests the presence of dust similar to that found in the "supergiant" shell of ionised filaments LMC 2, close to 30 Dor. The presence of the carriers of the UV bump (probably organic carbon and amorphous silicates) at 1 < z < 2.5 argues for outflows from asymptotic giant branch (AGB) stars being copious then. Consistent with their higher star-formation rates, the GMASS galaxies with a manifested UV bump are more luminous at rest-frame 8 μm, where the emission is dominated by polycyclic aromatic hydrocarbons (also products of AGB stars). In addition, they exhibit larger equivalent widths for prominent UV (metal) absorption features, mostly of interstellar origin, which indicates overall more evolved stellar populations. Conclusions. We conclude that diversification of the small-size dust component (responsible for the differential extinction at UV wavelengths and the emission at mid-IR wavelengths) has already started in the most evolved star-forming systems at 1 < z < 2.5.

The metal-enriched host of an energeticγ-ray burst atz ≈ 1.6

“…A metallicity of around solar was also inferred from GRB-DLAs for GRBs 070802 and 080607, both of which were substantially reddened, and had 2175 Å dust features (Elíasdóttir et al 2009;Prochaska et al 2009;Perley et al 2011b) as well. This seems to support the association between the 2175 Å bump and chemically evolved galaxies (e.g., Noll et al 2009). With only a small handful of such events, however, no strong conclusions can be drawn, yet.…”

GMASS ultradeep spectroscopy of galaxies atz ~ 2

“…We used the GMASS spectra and extensive photometry in the CDFS to perform several studies, including that of quiescent superdense galaxies at z > 1.4 Cappellari et al 2009), the stellar metallicity and outflows of star-forming z ∼ 2 galaxies (Halliday et al 2008;Talia et al 2012), the evolution of the rest-frame colour distribution and dust properties of high redshift galaxies Noll et al 2009), and the properties of galaxies in, and inflow of cold gas into, the galaxy overdensity at z = 1.6 (Kurk et al 2009;Giavalisco et al 2011). The public release of the GMASS spectra will facilitate further studies of the distant galaxies targeted by our survey.…”

“…They used the GMASS spectroscopy and photometry to show that the distribution of galaxies in the (U−B) colour vs. stellar mass plane is bimodal up to at least redshift z = 2. Noll et al (2009) measured the shape of the ultraviolet (UV) extinction curve in a sample of 78 galaxies from the GMASS survey at 1 < z < 2.5 and concluded that diversification of the smallsize dust component has already started in the most evolved starforming systems in this redshift range. In Kurk et al (2009), we described the properties of a structure of galaxies at z = 1.6, which form a strong peak in the redshift distribution within the GMASS field and an overdensity in redshift space by a factor of six.…”

First simultaneous optical/near-infrared imaging of an X-ray selected, high-redshift cluster of galaxies with GROND

“…We followed the indicated prescriptions for the model-dependent attenuation 9 of galaxy templates, so that a "Prevot extinction law" (Prevot et al 1984) was applied to SEDs numbered from 13 to 23, a so-called "Calzetti attenuation law" (Calzetti et al 2000) and two "modified" Calzetti attenuation laws (see Ilbert et al 2009) were applied to SEDs numbered from 23 to 31. This choice accounts for the fact that high-z starforming galaxies are characterized by extinction laws that differ at rest-frame ultraviolet wavelengths, as it is in the Local Group (Noll et al 2009 and references therein). In all cases, the reddening E(B − V) was enabled to range between 0 and 0.5 mag in steps of 0.05 mag.…”