Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDust in an extremely metal-poor galaxy: mid-infrared observations of SBS 0335-052
125
0
0.0
(
0
)
Authors
T.X. Thuan
Ask ChatGPT about the research
No Arabic abstract
The metal deficient (Z = Z_sun/41) Blue Compact Dwarf Galaxy (BCD) SBS 0335-052 was observed with ISOCAM between 5 and 17 mic. With a L_12mic/L_B ratio of 2.15, the galaxy is unexpectedly bright in the mid-infrared for such a low-metallicity object. The mid-infrared spectrum shows no sign of the Unidentified Infrared Bands, which we interpret as an effect of the destruction of their carriers by the very high UV energy density in SBS 0335-052. The spectral energy distribution (SED) is dominated by a very strong continuum which makes the ionic lines of [SIV] and [NeIII] very weak. From 5 to 17 mic, the SED can be fitted with a grey-body spectrum, modified by an extinction law similar to that observed toward the Galactic Center, with an optical depth of A_V~19-21 mag. Such a large optical depth implies that a large fraction (as much as ~ 75%) of the current star-formation activity in SBS 0335-052 is hidden by dust with a mass between 3x10^3 M_sun and 5x10^5 M_sun. Silicate grains are present as silicate extinction bands at 9.7 and 18 mic can account for the unusual shape of the MIR spectrum of SBS 0335-052. It is remarkable that such a nearly primordial environment contains as much dust as galaxies which are 10 times more metal-rich. If the hidden star formation in SBS 0335-052 is typical of young galaxies at high redshifts, then the cosmic star formation rate derived from UV/optical fluxes would be underestimated.
rate research
Read More
We present the results of HI mapping with the NRAO VLA of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, SBS 0335-052, with an oxygen abundance of only 1/40 that of the Sun. We study the structure and dynamics of the neutral gas in this chemically young object with a spatial resolution of 20.5x15 (~ 5.4 x 3.9 kpc at an assumed distance of 54.3 Mpc), a sensitivity at the 2sigma detection level of ~2.0K or 7.5x10^19 cm^-2 and a velocity resolution of 21.2 km s^-1. We detected a large HI complex associated with this object with an overall size of about 66 by 22 kpc and elongated in the East-West direction. There are two prominent, slightly resolved peaks visible in the integrated HI map, separated in the East-West direction by 22 kpc (84). The eastern peak is nearly coincident with the position of the optical galaxy SBS 0335-052. The western peak is about a factor of 1.3 brighter in the HI line and is identified with a faint blue compact dwarf galaxy, SBS 0335-052W, with m_B = 19.4, and a metallicity close to the lowest values known for BCDs, about 1/50 that of the Sun. The radial velocities of both systems are similar, suggesting that the two BCDs SBS 0335-052 and SBS 0335-052W constitute a pair of dwarf galaxies embedded in a common HI envelope. Alternatively, the BCDs can be the nuclei of two distinct interacting primordial HI clouds. The estimated total dynamical mass, assuming the BCDs form a bound system, is larger than 6x10^9 Msun. This is to be compared to a total gaseous mass M_gas = 2.1x10^9 Msun, and a total stellar mass Mstar < 10^8 Msun. Hence, the mass of the SBS 0335-052 system is dominated by dark matter (abridged).
We present two-dimensional spectroscopy of the extremely metal-deficient blue compact dwarf (BCD) galaxy SBS 0335-052E aiming to studyphysical conditions, element abundances and kinematical properties of the ionised gas in this galaxy. Observations were obtained in the spectral range 3620-9400A with the imaging spectrograph GIRAFFE installed on the UT2 of the Very Large Telescope (VLT). These observations are the first ones carried out so far with GIRAFFE in the ARGUS mode which allows to obtain simultaneously 308 spectra covering a 11.4x7.3 region. We produced images of SBS 0335-052E in the continuum and in emission lines of different stages of excitation. We find that while the maximum of emission in the majority of lines, including the strong lines Hbeta 4861A, Halpha 6563A, [OIII] 4363,5007A, [OII] 3726,3729A, coincides with the youngest south-eastern star clusters 1 and 2, the emission of HeII 4686A line is offset to the more evolved north-west clusters 4,5. This suggests that hard ionising radiation responsible for the HeII 4686A emission is not related to the most massive youngest stars, but rather is connected with fast radiative shocks. This conclusion is supported by the kinematical properties of the ionised gas from the different emission lines as the velocity dispersion in the HeII 4686A line is systematically higher, by ~50%-100%, than that in other lines. The variations of the emission line profiles suggest the presence of an ionised gas outflow in the direction perpendicular to the galaxy disk. (abridged)
We present 4-micron ISAAC imaging and spectroscopy of the extremely metal-poor dwarf galaxy SBS 0335-052, aimed at a better understanding of the dust in this low-metallicity galaxy. The 4-micron emission turns out to be very compact, confined to the brightest pair of Super Star Clusters (SSCs). The Ks-L$^prime$ color is extremely red, and the $L^prime$ emission is consistent with the extrapolation of the ISO mid-infrared spectral energy distribution (SED). From hydrogen recombination lines and a fit to the near-/mid-infrared SED, we confirm a visual extinction of >= 15 mag. Our data suggest that the sites of the optical and infrared emission are distinct: the optical spectral lines come from an almost dustless region with a high star formation rate and a few thousand OB stars. This region lies along the line-of-sight to a very dusty central star cluster in which there are more than three times as many massive stars, completely hidden in the optical. From the extinction, we derive an upper limit for the dust mass of 10^5 M$_odot$ which could be produced by recent supernovae.
We present an X-ray study of the three most metal-deficient blue compact dwarf (BCD) galaxies known in the local Universe, based on deep Chandra observations of SBS 0335-052 (0.025 solar abundance), SBS 0335-052W (0.02 solar abundance) and I Zw 18 (0.02 solar abundance). All three are detected, with more than 90% of their X-ray emission arising from point-like sources. The 0.5-10.0 keV luminosities of these point sources are in the range (1.3-8.5)x1e39 erg/s. We interpret them to be single or a collection of high-mass X-ray binaries, the luminosities of which may have been enhanced by the low metallicity of the gas. There are hints of faint extended diffuse X-ray emission in both SBS 0335-052 and I Zw 18, probably associated with the superbubbles visible in both BCDs. The spectrum of I Zw 18 shows a OVIII hydrogen-like emission line. The best spectral fit gives an O overabundance of the gas in the X-ray point source by a factor of ~7 with respect to the Sun, or a factor of ~350 with respect to the O abundance determined for the HII region.
The results of deep long-slit spectroscopy of the extremely low-metallicity blue compact dwarf (BCD) galaxy SBS 0335-052 are presented. Down to intensity levels of 10^{-3 ... -4} of Hbeta, unprecedented for spectroscopy of extra-galactic giant H II regions, we detect numerous weak permitted and forbidden nebular lines in the brightest part of the galaxy. With varying degrees of confidence, the detections include lines of high-ionization ions like Fe^{4+} -Fe^{6+}, implying very hard ionizing radiation. Two broad emission features, possibly from Wolf-Rayet stars, and stellar He II 4200 absorption are seen in the same region. The large spatial extent of He II 4686 emission (implying the presence of sufficient ionizing photons with energies above 54 eV) and the spatial distribution of the electron temperature suggest that at least some part of the hard radiation is associated with shocks. Extended Halpha emission is detected over ~ 6 - 8 kpc, a much larger area than in previous studies, suggesting that hot ionized gas is spread out far away from the central ionizing clusters. This shows that nebular line and continuous emission can significantly modify the colours of these extended regions and must be taken into account in studies of the underlying stellar population.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
