[Paper Review] New insights to the photometric structure of Blue Compact Dwarf Galaxies from deep Near-Infrared studies I. Observations, surface photometry and decomposition of surface brightness profiles

K. G. Noeske, P. Papaderos+2 more|GoeScholar The Publication Server of the Georg-August-Universität Göttingen (Georg-August-Universität Göttingen)|Jul 30, 2003

Galaxies: Formation, Evolution, PhenomenaPhysics and Astronomy103 references62 citations

TL;DR

This study presents deep near-infrared (NIR) imaging of Blue Compact Dwarf (BCD) galaxies, revealing extended low-surface brightness (LSB) host components previously obscured by intense starburst emission in optical data. Using surface photometry and profile decomposition, it identifies type V surface brightness profiles—characterized by central intensity depressions—in over half the sample, indicating significant structural complexity in the underlying stellar populations, with implications for photometric fading and evolutionary models of dwarf galaxies.

ABSTRACT

(shortened) We analyze deep Near Infrared (NIR) broad band images for a sample of Blue Compact Dwarf Galaxies (BCDs), allowing for the quantitative study of their extended stellar low-surface brightness (LSB) host galaxies. NIR surface brightness profiles (SBPs) of the LSB hosts agree at large galactocentric radii with those from optical studies. At small to intermediate radii, however, the NIR data reveal for more than half of our sample a significant flattening of the exponential SBP of the LSB host. Such SBPs ("type V" SBPs, Binggeli & Cameron 1991) have rarely been detected in LSB hosts of BCDs at optical wavelengths, where the relative flux contribution of the starburst is stronger than in the NIR and can hide such central intensity depressions of the LSB host. The structural properties, frequency and physical origin of type V LSB SBPs in BCDs and other dwarf galaxies have not yet been systematically studied. Nevertheless, their occurrence in a significant fraction of BCDs would impose important new constraints to the radial distribution of their stellar mass, and to the photometric fading of BCDs after the termination of star-forming activity. Both a modified exponential (Papaderos et al. 1996a) and the Sersic law give satisfactory empirical descriptions for type V SBPs. However, we argue that the practical applicability of Sersic fits to LSB SBPs of BCDs is limited by, e.g., the extreme sensitivity of the solutions to small SBP uncertainties. Most stellar LSB host galaxies in the sample show optical-NIR colors indicative of evolved stellar populations with subsolar metallicity. Unsharp-masked NIR images and optical-NIR maps reveal numerous morphological details, and cases of non-uniform dust absorption on spatial scales up to ~1 kpc.

Motivation & Objective

• To investigate the photometric structure of Blue Compact Dwarf (BCD) galaxies using deep near-infrared (NIR) imaging to resolve the underlying low-surface brightness (LSB) stellar component.
• To overcome the limitations of optical studies, where intense starburst emission obscures the LSB host, particularly within inner 1–3 exponential scale lengths.
• To systematically analyze the frequency, structural properties, and physical origin of type V surface brightness profiles (flattened exponential profiles) in the LSB components of BCDs.
• To test the suitability of empirical fitting functions—modified exponential and Sérsic laws—for modeling the complex surface brightness profiles of BCD host galaxies.
• To derive optical-NIR colors of the LSB host to infer the metallicity and evolutionary state of its stellar population, and to detect dust absorption patterns at kiloparsec scales.

Proposed method

• Acquired deep broad-band NIR images (J, H, K bands) of a sample of BCDs using the ESO NTT and Calar Alto 3.6m telescopes.
• Performed surface photometry on the NIR data to derive surface brightness profiles (SBPs) of the LSB host galaxies out to large galactocentric radii.
• Applied profile decomposition techniques to separate the starburst and LSB components, identifying deviations from pure exponential profiles.
• Classified SBPs according to Binggeli & Cameron (1991) types, focusing on type V profiles (flattened at small radii) indicating central intensity depressions.
• Fitted the LSB profiles with two models: a modified exponential function (Papaderos et al. 1996a) and the Sérsic law, assessing goodness of fit and sensitivity to sky subtraction errors.
• Combined NIR data with optical data to produce unsharp-masked images, revealing morphological features and non-uniform dust absorption on scales up to ~1 kpc.

Experimental results

Research questions

• RQ1 What is the structural morphology of the low-surface brightness (LSB) host galaxy in BCDs when observed in the near-infrared, where dust extinction and ionized gas emission are reduced?
• RQ2 How frequently do type V surface brightness profiles (central intensity depressions in otherwise exponential profiles) occur in the LSB components of BCDs, and what are their implications for the radial mass distribution and photometric fading?
• RQ3 To what extent do the observed NIR surface brightness profiles of BCDs differ from those derived in the optical, and what does this imply about the relative contribution of the starburst and evolved stellar populations?
• RQ4 Which empirical fitting function—modified exponential or Sérsic law—provides a more robust and reliable fit to the complex LSB profiles in BCDs, especially under observational uncertainties?
• RQ5 What do the optical-NIR colors of the LSB host galaxies reveal about the metallicity and evolutionary state of their stellar populations, and what evidence is there for non-uniform dust absorption at kiloparsec scales?

Key findings

• Deep NIR imaging reveals the extended low-surface brightness (LSB) host galaxy in all sample BCDs, with surface brightness profiles (SBPs) at large radii consistent with exponential decline and scale lengths matching those from optical studies.
• More than half of the sample BCDs exhibit type V surface brightness profiles—characterized by a flattening or central depression in the inner 1–3 exponential scale lengths—indicating a previously hidden structural complexity in the underlying stellar population.
• The occurrence of type V profiles in the LSB component is rare in optical studies due to overwhelming starburst emission, but becomes detectable in the NIR due to reduced dust extinction and lower ionized gas contamination.
• The modified exponential function (Papaderos et al. 1996a) provides a satisfactory fit to type V profiles and is more robust than the Sérsic law, which shows extreme sensitivity to sky subtraction and SBP derivation uncertainties.
• Most LSB host galaxies in the sample show optical-NIR colors consistent with an evolved stellar population of subsolar metallicity, with Tol 65 and Tol 1214-277 showing blue colors (B–J < 1.3 mag), indicating relatively young or metal-poor populations.
• Unsharp-masked NIR images reveal morphological features such as coherent clusters of compact stellar groups and non-uniform dust absorption on scales up to ~1 kpc, suggesting complex star formation histories and dust distribution patterns.