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Register a new userSurface photometry of LSB edge-on galaxies
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Authors
Dmitry Bizyaev
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We present results of surface photometry for eleven edge-on galaxies observed with the 6-m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. The photometric scale length, the scale height, and the central surface brightness of the stellar disks for the galaxies were found using photometric cuts made parallel to the major and the minor axes for each galaxy. We show that four galaxies in our sample that were visually classified as objects of lowest surface brightness in the Revised Flat Galaxies Catalog have LSB (low surface brightness) disks. Stellar disks of our LSB galaxies are thinner than HSB (high surface brightness) ones. There is a good correlation between the central surface brightness of the stellar disk and its ratio of vertical to radial scales. The ratio of the disk photometric scales enables us to estimate the mass of the spherical galactic subsystem using results from numerical modeling. Combining our results with published rotation curves we determined the mass of dark halos for the galaxies in our sample. The LSB galaxies tend to harbor relatively more massive spherical subsystems than those of HSBs. Indeed, we found no systematic difference between our LSB and HSB objects in dark halo masses considering it separately from the bulge. At the same time, the inferred mass/luminosity ratio for the LSB disks appears to be systematically higher, when compared to the ratio for HSB ones.
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Surface photometry at 3.6$mu$m is presented for 61 low surface brightness (LSB) galaxies ($mu_o < 19$ 3.6$mu$m mag arcsecs$^{-2}$). The sample covers a range of luminosity from $-$11 to $-$22 in $M_{3.6}$ and size from 1 to 25 kpc. The morphologies in the mid-IR are comparable to those in the optical with 3.6$mu$m imaging reaches similar surface brightness depth as ground-based optical imaging. A majority of the resulting surface brightness profiles are single exponential in shape with very few displaying upward or downward breaks. The mean $V-3.6$ color of LSB is 2.3 with a standard deviation of 0.5. Color-magnitude and two color diagrams are well matched to models of constant star formation, where the spread in color is due to small changes in the star formation rate (SFR) over the last 0.5 Gyrs as also suggested by the specific star formation rate measured by H$alpha$.
Photometric parameters of stellar disks and bulges for several edge-on galaxies from the Catalog of Flat Galaxies (FGC) were determined. We discuss a difference between photometric parameters of LSB and HSB galaxies from our sample. Also we present results of R CCD photometry of edge-on galaxy RFGC 3647. Deprojecting this galaxy we show that it has thin LSB disk (central surface brightness $22^m.2$ in R) and high ratio of radial to vertical scale lengths. It is shown that initially gaseous disk of the galaxy was unstable and its velocity dispersion was low. Stellar disk of this LSB galaxy was not heated significantly since that time.
We perform near-infrared photometry of a large sample of 49 superthin edge-on galaxies. These galaxies are selected based on optical photometry because of high radial-to-vertical scale ratio in their stellar disks. The Near Infrared (NIR) H and K observations were conducted with the cryogenic-cooled camera ASTRONIRCAM on the 2.5m telescope at the Caucasus Mountain Observatory of Lomonosov Moscow State University. A majority of galaxies in our sample show comparable or better photometric depth than the Sloan Digital Sky Survey (SDSS) optical images. We estimate the structural parameters of stellar disks in the galaxies and find that the NIR scale height of stellar disks is comparable to that estimated from the optical, SDSS g, r and i, whereas the H and K scale length of the stellar disks is significantly shorter than in the g, r and i. We investigate if a realistic distribution of dust alone can explain the difference in the scale length and find that in the majority of the galaxies the radial variation of the stellar population is actually responsible for the color distribution. The latter suggests a younger age of the disks periphery, and the inside out building up of stellar disks in the superthin galaxies.
(Abridged). Low metallicities, large gas-to-star mass ratios, and blue colors of most low surface brightness (LSB) galaxies imply that these systems may be younger than their high surface brightness counterparts. We seek to find observational signatures that can help to constrain the age of blue LSB galaxies. We use numerical hydrodynamic modelling to study the long-term (~13 Gyr) dynamical and chemical evolution of blue LSB galaxies adopting a sporadic scenario for star formation. Our models utilize various rates of star formation and different shapes of the initial mass function (IMF). We complement hydrodynamic modelling with population synthesis modelling to produce the integrated B-V colors and Halpha equivalent widths (EW(Ha)). We find that the mean oxygen abundances, B-V colors, EW(Ha), and the radial fluctuations in the oxygen abundance, when considered altogether, can be used to constrain the age of blue LSB galaxies if some independent knowledge of the IMF is available. Our modelling strongly suggests the existence of a minimum age for blue LSB galaxies. Model B-V colors and mean oxygen abundances set a tentative minimum age at 1.5-3.0 Gyr, whereas model EW(Ha) suggest a larger value of order 5-6 Gyr. The latter value may decrease somewhat, if blue LSB galaxies host IMFs with a truncated upper mass limit. We found no firm evidence that the age of blue LSB galaxies is significantly smaller than 13 Gyr.
We have derived oxygen and nitrogen abundances of a sample of late-type, low surface brightness (LSB) galaxies found in the Sloan Digital Sky Survey (SDSS). Furthermore, we have computed a large grid (5000 models) of chemical evolution models (CEMs) testing various time-scales for infall, baryon densities and several power-law initial mass functions (IMFs) as well. Because of the rather stable N/O-trends found both in CEMs (for a given IMF) and in observations, we find that the hypotheses that LSB galaxies have stellar populations dominated by low-mass stars, i.e., very bottom-heavy IMFs (see Lee et al. 2004), can be ruled out. Such models predict much too high N/O-ratios and generally too low O/H-ratios. We also conclude that LSB galaxies probably have the same ages as their high surface brightness counterparts, although the global rate of star formation must be considerably lower in these galaxies.
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