Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDo young galaxies exist in the Local Universe? - Red Giant Branch detection in the metal-poor dwarf SBS 1415+437
332
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present results from an HST/ACS imaging study of the metal-poor blue compact dwarf galaxy SBS 1415+437. It has been argued previously that this is a very young galaxy that started to form stars only less than 100 Myr ago. However, we find that the optical color-magnitude diagram prominently reveals asymptotic giant branch and red giant branch (RGB) stars. The brightness of the RGB tip yields a distance of 13.6 Mpc. The color of the RGB implies that its stars must be older than approximately 1.3 Gyr, with the exact age depending on the assumed metallicity and dust extinction. The number of RGB stars implies that most of the stellar mass resides in this evolved population. In view of these and other HST results for metal-poor galaxies it seems that the local Universe simply may not contain any galaxies that are currently undergoing their first burst of star formation.
rate research
Read More
We use integral field spectroscopic (IFS) observations from Gemini Multi-Object Spectrograph-North (GMOS-N) to analyse the ionised gas in the principal star-forming region in the blue compact dwarf galaxy SBS 1415+437. The IFS data enable us to map the weak auroral line [O III] $lambda$4363 at a spatial scale of $sim$6.5 pc across a region of $sim$143 $times$ 143 pc$^2$. This in turn allows us to use the robust direct T$_e$-method to map the ionic and elemental abundances of nitrogen (N) along with the alpha-elements, oxygen (O), neon (Ne), sulphur (S) and argon (Ar). We utilise these abundances to map the relative abundances of N, Ne, S and Ar with respect to O. We segment this predominantly photoionised region of study into elliptical annuli on the basis of the H$alpha$ flux distribution to study the variation of chemical abundances and their ratios, and find no significant chemical variation. We also perform chemical abundance analysis on the integrated spectra of the region under study and elliptical annuli within it. We find that the inferred abundances are in agreement with the median of the abundances obtained from the chemical abundance maps of the principal star-forming region and the mapped values within annuli.The finding has important implications for direct comparison with high-redshift observations, where spatial resolution is not available, and for a consistent approach to track chemical evolution across cosmic time.
Definitely, an affirmative answer to this question would have implications of fundamental importance for astrophysics (a new class of compact stars), and for the physics of strong interactions (deconfined phase of quark matter, and strange matter hypothesis). In the present work, we use observational data for the newly discovered millisecond X-ray pulsar SAX J1808.4-3658 and for the atoll source 4U 1728-34 to constrain the radius of the underlying compact stars. Comparing the mass-radius relation of these two compact stars with theoretical models for both neutron stars and strange stars, we argue that a strange star model is more consistent with SAX J1808.4-3658 and 4U 1728-34, and suggest that they are likely strange star candidates.
We have obtained accurate near-infrared photometry of the Tip of the Red Giant Branches in the Local Group galaxies Sculptor, NGC 6822, NGC 3109, IC 1613 and WLM. We have used the derived TRGB magnitudes together with the absolute magnitude calibration of the near-infrared TRGB magnitude of Valenti, Ferraro and Origlia to determine the distances of these five galaxies. The statis- tical errors in the distance moduli are typically 4%. The systematic uncertain- ties are dominated by the knowledge of the mean metallicities of the red giant branches, and are in the range of 5-8%. We observe a slight (2%) systematic difference between the distances derived from the J and K bands, respectively, which is within the 1 {sigma} errors of the distances. We compare the new distances derived in this paper with other recent distance determinations for our target galaxies and find excellent agreement. In particular, the near-infrared TRGB distances to the four dwarf irregular galaxies in the sample agree to better than 5% in each case with their Cepheid distances obtained from infrared photome- try, indicating that there is no appreciable systematic offset between these two fundamental techniques using old and young stellar populations, respectively.
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 optical properties of a number of supercompact ultraviolet luminous galaxies (UVLG), recently discovered in the local Universe matching GALEX and Sloan Digital Sky Survey (SDSS) data, are discussed. Detailed re-analysis of the SDSS data for these and other similar but nearer galaxies shows that their surface brightness radial profile in both R and u bands is in most cases well described by an extended disk plus a central unresolved component (possibly a bulge). Since the SDSS pipeline used a single disk component to derive the half light radius of these UVLGs their size was severely underestimated. Consequently, the average UV surface brightness is much lower that previously quoted casting doubts on the claim that UVLGs are the local analogs of high redshift Lyman break galaxies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
