Engineering topics

Salo, H

Publications and source records attributed to Salo, H.

4 records

DOE OSTI2012

DISSECTING EARLY-TYPE DWARF GALAXIES INTO THEIR MULTIPLE COMPONENTS

Early-type dwarf galaxies, once believed to be simple systems, have recently been shown to exhibit an intriguing diversity in structure and stellar content. To analyze this further, we started the SMAKCED project (Stellar content, MAss and Kinematics of Cluster Early-type Dwarfs, http://www.smakced.net) and obtained deep H-band images for 101 early-type dwarf galaxies in the Virgo Cluster in a brightness range of -19 mag {<=} M{sub r} {<=} -16 mag, typically reaching a signal-to-noise ratio of 1 per pixel of {approx}0.''25 at surface brightnesses {approx}22.5 mag arcsec{sup -2} in the H band. Here we present the first results of decomposing their two-dimensional light distributions. This is the first study dedicated to early-type dwarf galaxies using the two-dimensional multi-component decomposition approach, which has been proven to be important for giant galaxies. Armed with this new technique, we find more structural components than previous studies: only a quarter of the galaxies fall into the simplest group, namely, those represented by a single Sersic function, optionally with a nucleus. Furthermore, we find a bar fraction of 18%. We also detect a similar fraction of lenses which appear as shallow structures with sharp outer edges. Galaxies with bars and lenses are found to be more concentrated toward the Virgo galaxy center than the other sample galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

DECREASED FREQUENCY OF STRONG BARS IN S0 GALAXIES: EVIDENCE FOR SECULAR EVOLUTION?

Using data from the Near-Infrared S0 Survey of nearby, early-type galaxies, we examine the distribution of bar strengths in S0 galaxies as compared to S0/a and Sa galaxies, and as compared to previously published bar strength data for Ohio State University Bright Spiral Galaxy Survey spiral galaxies. Bar strengths based on the gravitational torque method are derived from 2.2 {mu}m K{sub s} -band images for a statistical sample of 138 (98 S0, 40 S0/a,Sa) galaxies having a mean total blue magnitude (B{sub T}) {<=} 12.5 and generally inclined less than 65{sup 0}. We find that S0 galaxies have weaker bars on average than spiral galaxies in general, even compared to their closest spiral counterparts, S0/a and Sa galaxies. The differences are significant and cannot be entirely due to uncertainties in the assumed vertical scale heights or in the assumption of constant mass-to-light ratios. Part of the difference is likely simply due to the dilution of the bar torques by the higher mass bulges seen in S0s. If spiral galaxies accrete external gas, as advocated by Bournaud and Combes, then the fewer strong bars found among S0s imply a lack of gas accretion according to this theory. If S0s are stripped former spirals, or else are evolved from former spirals due to internal secular dynamical processes which deplete the gas as well as grow the bulges, then the weaker bars and the prevalence of lenses in S0 galaxies could further indicate that bar evolution continues to proceed during and even after gas depletion.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

RING STAR FORMATION RATES IN BARRED AND NONBARRED GALAXIES

Nonbarred ringed galaxies are relatively normal galaxies showing bright rings of star formation in spite of lacking a strong bar. This morphology is interesting because it is generally accepted that a typical galactic disk ring forms when material collects near a resonance, set up by the pattern speed of a bar or bar-like perturbation. Our goal in this paper is to examine whether the star formation properties of rings are related to the strength of a bar or, in the absence of a bar, to the non-axisymmetric gravity potential in general. For this purpose, we obtained H{alpha} emission line images and calculated the line fluxes and star formation rates (SFRs) for 16 nonbarred SA galaxies and four weakly barred SAB galaxies with rings. For comparison, we combine our new observations with a re-analysis of previously published data on five SA, seven SAB, and 15 SB galaxies with rings, three of which are duplicates from our sample. With these data, we examine what role a bar may play in the star formation process in rings. Compared to barred ringed galaxies, we find that the inner ring SFRs and H{alpha}+[N II] equivalent widths in nonbarred ringed galaxies show a similar range and trend with absolute blue magnitude, revised Hubble type, and other parameters. On the whole, the star formation properties of inner rings, excluding the distribution of H II regions, are independent of the ring shapes and the bar strength in our small samples. We confirm that the deprojected axis ratios of inner rings correlate with maximum relative gravitational force Q{sub g} ; however, if we consider all rings, a better correlation is found when a local bar forcing at the radius of the ring, Q{sub r} , is used. Individual cases are described and other correlations are discussed. By studying the physical properties of these galaxies, we hope to gain a better understanding of their placement in the scheme of the Hubble sequence and how they formed rings without the driving force of a bar.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2010

BARS DO DRIVE SPIRAL DENSITY WAVES

Recently, Buta et al. examined the question 'Do Bars Drive Spiral Density Waves?', an idea supported by theoretical studies and also from a preliminary observational analysis. They estimated maximum bar strengths Q{sub b} , maximum spiral strengths Q{sub s} , and maximum m = 2 arm contrasts A {sub 2s} for 23 galaxies with deep Anglo-Australian Telescope (AAT) K{sub s} -band images. These were combined with previously published Q{sub b} and Q{sub s} values for 147 galaxies from the Ohio State University Bright Spiral Galaxy Survey (OSUBSGS) sample and with the 12 galaxies from Block et al. Weak correlation between Q{sub b} and Q{sub s} was confirmed for the combined sample, whereas the AAT subset alone showed no significant correlations between Q{sub b} and Q{sub s} , nor between Q{sub b} and A {sub 2s}. A similar negative result was obtained in Durbala et al. for 46 galaxies. Based on these studies, the answer to the above question remains uncertain. Here we use a novel approach, and show that although the correlation between the maximum bar and spiral parameters is weak, these parameters do correlate when compared locally. For the OSUBSGS sample, a statistically significant correlation is found between the local spiral amplitude, and the forcing due to the bar's potential at the same distance, out to {approx}1.6 bar radii (the typical bar perturbation is then of the order of a few percent). Also for the sample of 23 AAT galaxies of Buta et al., we find a significant correlation between local parameters out to {approx}1.4 bar radii. Our new results confirm that, at least in a statistical sense, bars do indeed drive spiral density waves.

79 ASTRONOMY AND ASTROPHYSICS↗