Astronomy
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Browsing Astronomy by Subject "galaxies: elliptical and lenticular, cD"
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Item Exploring the correlations between globular cluster populations and supermassive black holes in giant galaxies(The American Astronomical Society, 2012) Rhode, K.L.This paper presents an analysis of the correlation between the number of globular clusters ($N_{GC}$) in giant galaxies and the mass of the galaxies' central supermassive black hole ( $M_{SMBH}$). I construct a sample of 20 elliptical, spiral, and S0 galaxies with known SMBH masses and with accurately measured GC system properties derived from wide-field imaging studies. The coefficients of the best-fitting $N_{GC}-M_{SMBH}$ relation for the early-type galaxies are consistent with those from previous work but in some cases have smaller relative errors. I examine the correlation between $N_{GC}$ and $M_{SMBH}$ for various subsamples and find that elliptical galaxies show the strongest correlation, while S0 and pseudobulge galaxies exhibit increased scatter. I also compare the quality of the fit of the numbers of metal-poor GCs versus SMBH mass and the corresponding fit for metal-rich GCs. I supplement the 20 galaxy sample with 10 additional galaxies with reliable $N_{GC}$ determinations but without measured $M_{SMBH}$. I use this larger sample to investigate correlations between $N_{GC}$ and host galaxy properties like total galaxy luminosity and stellar mass, and bulge luminosity and mass. I find that the tightest correlation is between $N_{GC}$ and total galaxy stellar mass. This lends support to the notion that $N_{GC}$ and $M_{SMBH}$ are not directly linked but are correlated because both quantities depend on the host galaxy potential. Finally, I use the $N_{GC}-M_{SMBH}$ relation derived from the 20 galaxy sample to calculate predicted $M_{SMBH}$ values for the 10 galaxies with accurate $N_{GC}$ measurements but without measured SMBH masses.Item Galaxy-scale star formation on the red sequence: The continued growth of S0s and the quiescence of ellipticals(The American Astronomical Society, 2012) Salim, S.; Fang, J.J.; Rich, R.M.; Faber, S.M.; Thilker, D.A.This paper examines star formation (SF) in relatively massive, primarily early-type galaxies (ETGs) at $z \sim 0.1$. A sample is drawn from bulge-dominated Galaxy Evolution Explorer/Sloan Digital Sky Survey (GALEX/SDSS) galaxies on the optical red sequence with strong UV excess and yet quiescent SDSS spectra. High-resolution far-UV imaging of 27 such ETGs using Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel (ACS/SBC) reveals structured UV morphology in 93% of the sample, consistent with low-level ongoing SF ($\sim0.5 M_{\odot} yr^{–1}$). In 3/4 of the sample the SF is extended on galaxy scales (25-75 kpc), while the rest contains smaller (5-15 kpc) SF patches in the vicinity of an ETG—presumably gas-rich satellites being disrupted. Optical imaging reveals that all ETGs with galaxy-scale SF in our sample have old stellar disks (mostly S0 type). None is classified as a true elliptical. In our sample, galaxy-scale SF takes the form of UV rings of varying sizes and morphologies. For the majority of such objects we conclude that the gas needed to fuel current SF has been accreted from the intergalactic medium, probably in a prolonged, quasi-static manner, leading in some cases to additional disk buildup. The remaining ETGs with galaxy-scale SF have UV and optical morphologies consistent with minor merger-driven SF or with the final stages of SF in fading spirals. Our analysis excludes that all recent SF on the red sequence resulted from gas-rich mergers. We find further evidence that galaxy-scale SF is almost exclusively an S0 phenomenon ($\sim$20% S0s have SF) by examining the overall optically red SDSS ETGs. Conclusion is that significant number of field S0s maintain or resume low-level SF because the preventive feedback is not in place or is intermittent. True ellipticals, on the other hand, stay entirely quiescent even in the field.Item The globular cluster populations of giant galaxies: Mosaic imaging of five moderate-luminosity early-type galaxies(The American Astronomical Society, 2012) Hargis, J.R.; Rhode, K.L.This paper presents results from wide-field imaging of the globular cluster (GC) systems of five intermediate-luminosity ($M_{V}$ ~ –21 to –22) early-type galaxies. The aim is to accurately quantify the global properties of the GC systems by measuring them out to large radii. We obtained BVR imaging of four lenticular galaxies (NGC 5866, NGC 4762, NGC 4754, NGC 3384) and one elliptical galaxy (NGC 5813) using the KPNO 4 m telescope and Mosaic imager and traced the GC population to projected galactocentric radii ranging from ~20 kpc to 120 kpc. We combine our imaging with Hubble Space Telescope data to measure the GC surface density close to the galaxy center. We calculate the total number of GCs (N GC) from the integrated radial profile and find $N_{GC}$ = 340 ± 80 for NGC 5866, $N_{GC}$ = 2900 ± 400 for NGC 5813, $N_{GC}$ = 270 ± 30 for NGC 4762, $N_{GC}$ = 115 ± 15 for NGC 4754, and $N_{GC}$ = 120 ± 30 for NGC 3384. The measured GC specific frequencies are SN between 0.6 and 3.6 and T in the range 0.9-4.2. These values are consistent with the mean specific frequencies for the galaxies' morphological types found by our survey and other published data. Three galaxies (NGC 5866, NGC 5813, and NGC 4762) had sufficient numbers of GC candidates to investigate color bimodality and color gradients in the GC systems. NGC 5813 shows strong evidence (>3σ) for bimodality and a B – R color gradient resulting from a more centrally concentrated red (metal-rich) GC subpopulation. We find no evidence for statistically significant color gradients in the other two galaxies.Item Globular cluster systems of spiral and S0 galaxies: Results from WIYN imaging of NGC1023, NGC1055, NGC7332, and NGC7339(The American Astronomical Society, 2012) Young, M.D.; Dowell, J.L.; Rhode, K.L.We present results from a study of the globular cluster (GC) systems of four spiral and S0 galaxies imaged as part of an ongoing wide-field survey of the GC systems of giant galaxies. The target galaxies - the SB0 galaxy NGC1023, the SBb galaxy NGC1055, and an isolated pair comprised of the Sbc galaxy NGC7339 and the S0 galaxy NGC7332 - were observed in BVR filters with the WIYN 3.5m telescope and Minimosaic camera. For two of the galaxies, we combined the WIYN imaging with previously published data from the $\textit{Hubble Space Telescope}$ and the Keck Observatory to help characterize the GC distribution in the central few kiloparsecs. We determine the radial distribution (surface density of GCs versus projected radius) of each galaxy's GC system and use it to calculate the total number of GCs ($N_{GC}$). We find $N_{GC}$ = 490 ± 30, 210 ± 40, 175 ± 15, and 75 ± 10 for NGC1023, NGC1055, NGC7332, and NGC7339, respectively. We also calculate the GC specific frequency (N GC normalized by host galaxy luminosity or mass) and find values typical of those of the other spiral and E/S0 galaxies in the survey. The two lenticular galaxies have sufficient numbers of GC candidates for us to perform statistical tests for bimodality in the GC color distributions. We find evidence at a high confidence level (>95%) for two populations in the $B - R$ distribution of the GC system of NGC1023. We find weaker evidence for bimodality (>81% confidence) in the GC color distribution of NGC7332. Finally, we identify eight GC candidates that may be associated with the Magellanic dwarf galaxy NGC1023A, which is a satellite of NGC1023.Item The slow death (or rebirth?) of extended star formation in $z \sim 0.1$ green valley early-type galaxies(The American Astronomical Society, 2012) Fang, J.J.; Faber, S.M.; Salim, S.; Graves, G.J.; Rich, R.M.UV observations in the local universe have uncovered a population of early-type galaxies with UV flux consistent with low-level recent or ongoing star formation. Understanding the origin of such star formation remains an open issue. We present resolved UV-optical photometry of a sample of 19 Sloan Digital Sky Survey (SDSS) early-type galaxies at $z \sim 0.1$ drawn from the sample originally selected by Salim & Rich to lie in the bluer part of the green valley in the UV-optical color-magnitude diagram as measured by the $\textit{Galaxy Evolution Explorer (GALEX)}$. Utilizing high-resolution $\textit{Hubble Space Telescope (HST)}$ far-UV imaging provides unique insight into the distribution of UV light in these galaxies, which we call "extended star-forming early-type galaxies" (ESF-ETGs) because of extended UV emission that is indicative of recent star formation. The UV-optical color profiles of all ESF-ETGs show red centers and blue outer parts. Their outer colors require the existence of a significant underlying population of older stars in the UV-bright regions. An analysis of stacked SDSS spectra reveals weak LINER-like emission in their centers. Using a cross-matched SDSS DR7/$GALEX$ GR6 catalog, we search for other green valley galaxies with similar properties to these ESF-ETGs and estimate that $\approx 13%$ of dust-corrected green valley galaxies of similar stellar mass and UV-optical color are likely ESF-candidates, i.e., ESF-ETGs are not rare. Our results are consistent with star formation that is gradually declining in existing disks, i.e., the ESF-ETGs are evolving onto the red sequence for the first time, or with rejuvenated star formation due to accreted gas in older disks provided that the gas does not disrupt the structure of the galaxy and the resulting star formation is not too recent and bursty. ESF-ETGs may typify an important subpopulation of galaxies that can linger in the green valley for up to several Gyrs, based on their resemblance to nearby gas-rich green valley galaxies with low-level ongoing star formation.