Optical and infrared observations of the young SMC blob N26 and its environment

Abstract

Context. High-excitation compact H  regions of the Magellanic Clouds are sites of recent massive star formation in low metallicity environments. Aims. Detailed study of these regions and their environments using high-spatial resolution observations is necessary to better understand massive star formation, which is still an unsolved problem. We aim at a detailed study of the Small Magellanic Cloud compact H  region N26, which is only ∼4 in diameter.Methods. This study is based on high spatial resolution imaging (∼0. 1-0. 3) in JHKs and L bands, using the VLT equipped with the NAOS adaptive optics system. A larger region (∼50 pc × 76 pc) was also imaged at medium spatial resolution, using the ESO 2.2 m telescope in optical wavelengths. We also used the JHKs archival data from the IRSF survey and the Spitzer Space Telescope SAGE-SMC survey. Results. Our high-resolution JHKs data of the compact high-excitation H  region N26 reveal a new, bright component (C) between the two already known optical components A and B. Components A and C are resolved into several stars. Component A is the main ionization source of N26 and coincides with the radio continuum source B0046-7333. A new compact H  region with very faint [O ] λ5007 emission has been discovered. In the mid-infrared, our field resembles a shell formed by filaments and dust clumps, coinciding with the molecular cloud SMCB2. Region N22, located in the center of the shell, is the most excited H  region of the complex and seems to have created a cavity in SMCB2. We derive nebular parameters from spectra, and using color-magnitude and color-color diagrams, we identify stellar sources that show significant near-infrared excess emission in order to identify the best YSO candidates.

Carbon gas in SMC low-metallicity star-forming regions

“…Beam dilution decreases this even further to N C ≤ 5 × 10 15 cm −2 . For the source complex N 25+N 26 the numbers are less clear, but we estimate in a similar way from the radio flux (Filipović et al 2002) and the electron densities (≈10 3 cm −3 - Testor et al 2014) an emission measure E.M. = 7 × 10 4 pc cm −6 and column densities N H = 2 × 10 20 cm −2 , from which we find N C ≤ 2 × 10 15 cm −2 once again after taking beam dilution into account. In either case, the contribution of the H II region to the (ionized) carbon column density is not more than 2−5 per cent.…”

“…N 25 is one of a group of H II regions also containing the compact N 26, the large and diffuse N 22, and N 21 and N 23 (Testor 2001;Testor et al 2014) in the crowded southwestern SMC Bar. The ionization of each of the nebulae appears to be dominated by a single O star.…”

A dearth of young and bright massive stars in the Small Magellanic Cloud

“…Embedded young massive stars can manifest themselves as YSOs or (ultra-)compact H II regions (see, e.g., Heydari-Malayeri et al 2002;Testor et al 2014, for examples of the latter). Both are known to be quite numerous in the SMC.…”

Identification of Herbig Ae/Be Stars in the Small Magellanic Cloud

“…Kamath et al (2014) identified 63 stellar sources in the SMC that appear to be intermediate-mass YSOs, of which 27 exhibit optical line emission, and 23 exhibit strong UV excesses. Testor et al (2014) identified 12 massive YSO candidates in the H II region N26 in the SMC using infrared and optical imaging and spectroscopy. Ruffle et al (2015) introduced a systematic method for classifying mid-infrared (MIR) point sources in the SMC, identifying 10 sources as candidate HAeBe stars (YSO-4 in their classification system) and Ward et al (2017) recently obtained NIR spectra of 17 massive YSOs in the SMC identifying extended molecular hydrogen and Brγ emission, enabling a comparison of SMC and Galactic YSOs.…”