VLT/X-shooter observations of blue compact galaxies Haro 11 and ESO 338-IG 004

Abstract

Context. Strongly star-forming galaxies of subsolar metallicities are typical of the high-redshift universe. Here we therefore provide accurate data for two low-z analogs, the well-known low-metallicity emission-line galaxies Haro 11 and ESO 338-IG 004. Aims. Our main goal is to derive their spectroscopic properties and to examine whether a previously reported near-infrared (NIR) excess in Haro 11 can be confirmed. Methods. On the basis of Very Large Telescope/X-shooter spectroscopic observations in the wavelength range ∼λλ3000-24 000 Å, we use standard direct methods to derive physical conditions and element abundances. Furthermore, we use X-shooter data together with Spitzer observations in the mid-infrared range to attempt to find hidden star formation. Results. We derive interstellar oxygen abundances of 12 + log O/H = 8.33 ± 0.01, 8.10 ± 0.04, and 7.89 ± 0.01 in the two H ii regions B and C of Haro 11 and in ESO 338-IG 004, respectively. The observed fluxes of the hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value of the extinction coefficient C(Hβ) across the entire wavelength range from the near-ultraviolet to the NIR and mid-infrared for each of the studied H ii regions. Thus, we confirm our previous findings obtained for several low-metallicity emission-line galaxies (Mrk 59, II Zw 40, Mrk 71, Mrk 996, SBS 0335-052E, PHL 293B, and GRB HG 031203) that the extinction coefficient C(Hβ) is not higher in the NIR than in the optical range and therefore that there are no emission-line regions contributing to the line emission in the NIR range, which are hidden in the optical range. The agreement between the extinction-corrected and CLOUDY-predicted fluxes implies that a H ii region model including only stellar photoionisation is able to account for the observed fluxes, in both the optical and NIR ranges. No additional excitation mechanism such as shocks from stellar winds and supernova remnants is needed. All observed spectral energy distributions (SEDs) can be reproduced quite well across the whole wavelength range by model SEDs except for Haro 11B, where there is a continuum flux excess at wavelengths >1.6 μm. It is possible that one or more red supergiant stars are responsible for the NIR flux excess in Haro 11B. We find evidence of a luminous blue variable (LBV) star in Haro 11C.

Using Lyman-αto detect galaxies that leak Lyman continuum

“…ratios are ∼4 and ∼12, respectively (Guseva et al 2012;Izotov et al 2009). However, SBS 0335−052 is a Lyα absorber (Thuan & Izotov 1997), and therefore our Lyα emission profile diagnostics are not applicable.…”

“…[ Guseva et al 2012) ratio is moderate, as is its LyC escape fraction f LyC esc = 0.032 derived from direct LyC measurement, and f LyC esc = 0.024 derived from the LIS absorption lines (Leitet et al 2013). …”

LIGHTING THE DARK MOLECULAR GAS: H2 AS A DIRECT TRACER

“…CGCG 007-025 is the lowest-metallicity galaxy in our dwarf sample with a value of [ ] + 12 log O H =7.77 (Izotov et al 2007). Guseva et al (2012) For selected SINGS galaxies, the metallicity values in the circumnuclear regions, which are approximately the size of our H 2 line flux extracted regions, are estimated by averaging the theoretical (KK04) and an empirical metallicity calibration (PTO5) as recommended by Moustakas et al (2010).…”

The nature of the interstellar medium of the starburst low-metallicity galaxy Haro 11: a multi-phase model of the infrared emission

“…Haro 11 -also know as ESO 350-IG38 -is a blue compact dwarf (BCD) galaxy located at 84 Mpc, with M B = −20.3, and metallicity Z ∼ 1/3 Z (Guseva et al 2012). It is composed of 3 main star-forming regions, or knots, described in Vader et al (1993) and Kunth et al (2003), with a morphology presumably resulting from a merger event (Östlin et al 2001).…”