Deep multiband surface photometry on a sample of 24 blue compact galaxies – I

Abstract

We present deep optical and near-infrared (NIR) U BV RIHKs imaging data for 24 blue compact galaxies (BCGs). The individual exposure times are on average ∼ 40 minutes in the optical (B) and ∼ 90 minutes in the NIR, but on occasion up to ∼ 5 hours for a single target and filter, observed on 2.5, 3.5, 8.2-m telescopes. The sample contains luminous dwarf and intermediate-mass BCGs which are predominantly metal-poor, although a few have near-solar metallicities. We have analyzed isophotal and elliptical integration surface brightness and color profiles, extremely deep (µ B 29 mag arcsec −2 ) contour maps and RGB images for each galaxy in the sample, and provide a morphological classification where such is missing. We have measured the total galaxy colors, the colors of the underlying host galaxy, and the colors of the burst, and compare these to the predictions of new state-of-the-art spectral evolutionary models (SEMs) both with and without contribution by nebular emission. Separating the burst from the underlying host we find that regardless of the total luminosity the host galaxy has the properties of a low surface brightness (LSB) dwarf with M B −18. For a number of galaxies we discover a distinct LSB component dominant around and beyond the Holmberg radius. For the specific case of ESO400-43A&B we detect an optical bridge between the two companion galaxies at the µ V ∼ 28th mag arcsec −2 isophotal level. Synthetic disk tests are performed to verify that we can trace such faint components with negligible errors down to µ B = 28 mag arcsec −2 and µ K = 23 mag arcsec −2 . By examining the structural parameters (central surface brightness µ 0 and scale length h r ) derived from two radial ranges typically assumed to be dominated by the underlying host galaxy, we demonstrate the importance of sampling the host well away from the effects of the burst. We find that µ 0 and h r of the BCGs host deviate from those of dwarf ellipticals (dE) and dwarf irregulars (dI) solely due to a strong burst contribution to the surface brightness profile almost down to the Holmberg radius. Structural parameters obtained from a fainter region, µ B = 26-28 mag arcsec −2 , are consistent with those of true LSB galaxies for the starbursting BCGs in our sample, and with dEs and dIs for the BCGs with less vigorous star formation.

Deep multiband surface photometry on a sample of 24 blue compact galaxies

“…it is not possible to distinguish between luminous blue compact galaxies and the less vigorously star forming galaxies of this sample in this parameter space. This is interesting considering the otherwise very different behavior and structural parameters of the galaxies in this paper and the luminous blue compacts of Micheva et al (2013). …”

“…Alternative measures of asymmetry, already introduced in Micheva et al (2013), are shown in Table 11, namely the Holmberg (A H ) and the dynamical (A dyn ) asymmetry. A H is calculated over images smoothed by a boxcar average filter of 1 × 1 kpc from the area enclosed by the Holmberg radius at µ = 26.5 mag arcsec −2 in the optical and R 23 at µ = 23 mag arcsec −2 in the NIR.…”

The Lyman alpha reference sample

“…A comparison between these radii gives an idea of the distribution of the light in the galaxy. We also estimated asymmetry (A), concentration (C), clumpiness (S), Gini coefficient (G), and second-order moment of the brightest 20% of the galaxy's flux (M20, see e.g., Conselice 2003;Lotz et al 2004;Scarlata et al 2007;Micheva et al 2013).…”

“…We measured fluxes at SExtractor centroid within elliptical apertures, by using the ELLIPSE task in ira f.stsdas.isophote and within circular apertures, by using the PHOT task in ira f.digiphot.apphot. ELLIPSE and PHOT outputs served to infer sizes, A, and C at minimum asymmetry (C minA ), as explained in Appendix A and previously adopted in Bershady et al (2000), Conselice (2003), Micheva et al (2013).…”

Molecular gas in low-metallicity starburst galaxies:

“…This conclusion relies mostly upon the detection of a more extended, evolved low-surface brightness host galaxy (Papaderos et al 1996a,b;Cairós et al 2001aCairós et al , 2003Noeske et al 2003Noeske et al , 2005Caon et al 2005;Gil de Paz & Madore 2005;Vaduvescu et al 2006;Hunter & Elmegreen 2006;Amorín et al 2007Amorín et al , 2009Micheva et al 2013). Nonetheless, even though they are not pristine galaxies, nearby BCDs constitute ideal laboratories for studying vigorous star formation and galaxy evolution in great detail, under physical conditions that are comparable to those present in low-mass galaxies at higher redshift (e.g., Amorín et al 2015Amorín et al , 2014aMaseda et al 2014;de Barros et al 2016).…”