The MOSDEF Survey: The First Direct Measurements of the Nebular Dust Attenuation Curve at High Redshift*

Abstract

We use a sample of 532 star-forming galaxies at redshifts z ; 1.4-2.6 with deep rest-frame optical spectra from the MOSFIRE Deep Evolution Field (MOSDEF) survey to place the first constraints on the nebular attenuation curve at high redshift. Based on the first five low-order Balmer emission lines detected in the composite spectra of these galaxies (Hα through  H), we derive a nebular attenuation curve that is similar in shape to that of the Galactic extinction curve, suggesting that the dust covering fraction and absorption/scattering properties along the lines of sight to massive stars at high redshift are similar to those of the average Milky Way sight line. The curve derived here implies nebular reddening values that are, on average, systematically larger than those derived for the stellar continuum. In the context of stellar population synthesis models that include the effects of stellar multiplicity, the difference in reddening of the nebular lines and stellar continuum may imply molecular cloud crossing timescales that are a factor of3 longer than those inferred for local molecular clouds, star formation rates that are constant or increasing with time such that newly formed and dustier OB associations always dominate the ionizing flux, and/or that the dust responsible for reddening the nebular emission may be associated with nonmolecular (i.e., ionized and neutral) phases of the interstellar medium. Our analysis points to a variety of investigations of the nebular attenuation curve that will be enabled with the next generation of ground-and space-based facilities.

The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

“…Stellar masses and rest-frame UV luminosities are obtained from spectral energy distribution (SED) fitting using the MAGPHYS code (da Cunha et al 2008) applied to aperture-corrected photometry from spanning ≈ 0.3 − 5 𝜇m in the wellstudied COSMOS field. Nebular attenuation, 𝐸 (𝐵 −𝑉), is estimated from the Balmer decrement based on H𝛼/H𝛽 following Reddy et al (2020). For further details we refer readers to Matthee et al (2021).…”

The NIRVANDELS Survey: a robust detection of α-enhancement in star-forming galaxies at z ≃ 3.4

“…As shown byReddy et al (2020), the nebular attenuation law in highredshift star-forming galaxies closely follows theCardelli et al (1989) Milky Way extinction curve.5 To convert SFRs from the Kroupa (2001) IMF assumed inHao et al (2011) to a Chabrier (2003) IMF we divide by 1.06.…”

Optical tweezers in a dusty universe

“…These observations may be carried out at a very wide range of wavelengths, from X-rays to radio waves, but traditionally the most important and defining data have come from the infrared, visible, and ultraviolet parts of the spectrum, summarized through a wavelength-dependent extinction curve along the lines of sight to individual stars. There are detailed extinction measurements along hundreds of lines of sight in the Milky Way Galaxy [35] and less accurate extinction data for the interstellar media of external galaxies [36]. Such observed extinction profiles are different, but are clearly members of the same family showing a basic similarity in their shapes: The extinction typically increases from low values in the infrared to high values in the far ultraviolet, a near-linear portion in the optical region, (in most cases) a pronounced and broad "bump" near 217.5 nm, and a final rise of varying slope into the far ultraviolet.…”