Testing the presence of multiple photometric components in nearby early-type galaxies using SDSS

We investigate two-dimensional image decomposition of nearby, morphologically selected early-type galaxies (ETGs). We are motivated by recent observational evidence of significant size growth of quiescent galaxies and theoretical development advocating a two-phase formation scenario for ETGs. We find that a significant fraction of nearby ETGs show changes in isophotal shape that require multi-component models. The characteristic sizes of the inner and outer component are $\sim 3$ and $\sim 15$ kpc. The inner component lies on the mass-size relation of ETGs at $z \sim 0.25-0.75$, while the outer component tends to be more elliptical and hints at a stochastic buildup process. We find real physical differences between the single- and double-component ETGs, with the double-component galaxies being younger and more metal-rich. The fraction of double component ETGs increases with increasing $\sigma$ and decreases in denser environments. We hypothesize that double-component systems were able to accrete gas and small galaxies until later times, boosting their central densities, building up their outer parts, and lowering their typical central ages. In contrast, the oldest galaxies, perhaps due to residing in richer environments, have no remaining hints of their last accretion episode.Comment: resubmitted to ApJ after referee's repor

The extended narrow-line region of two type-I quasi-stellar objects

We investigate the narrow-line region (NLR) of two radio-quiet QSOs, PG1012+008 and PG1307+085, using high signal-to-noise spatially resolved long-slit spectra obtained with FORS1 at the Very Large Telescope. Although the emission is dominated by the point-spread function of the nuclear source, we are able to detect extended NLR emission out to several kpc scales in both QSOs by subtracting the scaled central spectrum from outer spectra. In contrast to the nuclear spectrum, which shows a prominent blue wing and a broad line profile of the [O III] line, the extended emission reveals no clear signs of large scale outflows. Exploiting the wide wavelength range, we determine the radial change of the gas properties in the NLR, i.e., gas temperature, density, and ionization parameter, and compare them with those of Seyfert galaxies and type-II QSOs. The QSOs have higher nuclear temperature and lower electron density than Seyferts, but show no significant difference compared to type-II QSOs, while the ionization parameter decreases with radial distance, similar to the case of Seyfert galaxies. For PG1012+008, we determine the stellar velocity dispersion of the host galaxy. Combined with the black hole mass, we find that the luminous radio-quiet QSO follows the local M_BH-sigma* relation of active galactic nuclei.Comment: 7 pages, 5 figures, accepted for publication in Ap

Spectroscopy of the Young Stellar Association Price-Whelan 1: Origin in the Magellanic Leading Arm and Constraints on the Milky Way Hot Halo

We report spectroscopic measurements of stars in the recently discovered young stellar association Price-Whelan 1 (PW 1), which was found in the vicinity of the Leading Arm (LA) of the Magellanic Stream. We obtained Magellan+MIKE high-resolution spectra of the 28 brightest stars in PW 1 and used The Cannon to determine their stellar parameters. We find that the mean metallicity of PW 1 is [Fe/H]=-1.23 with a small scatter of 0.06 dex and the mean radial velocity is Vhelio=276.7 km/s with a dispersion of 11.0 km/s. Our results are consistent in Teff, logg, and [Fe/H] with the young and metal-poor characteristics (116 Myr and [Fe/H]=-1.1) determined for PW 1 from our discovery paper. We find a strong correlation between the spatial pattern of the PW 1 stars and the LA II gas with an offset of -10.15 deg in L_MS and +1.55 deg in B_MS. The similarity in metallicity, velocity, and spatial patterns indicates that PW 1 likely originated in LA II. We find that the spatial and kinematic separation between LA II and PW 1 can be explained by ram pressure from Milky Way gas. Using orbit integrations that account for the LMC and MW halo and outer disk gas, we constrain the halo gas density at the orbital pericenter of PW 1 to be n_halo (17 kpc) = 2.7 (3) x 10^-3 atoms/cm^3 and the disk gas density at the midplane at 20 kpc to be n_disk (20 kpc,0) = 6.0 (1.8) x 10^-2 atoms/cm^3. We, therefore, conclude that PW 1 formed from the LA II of the Magellanic Stream, making it a powerful constraint on the Milky Way-Magellanic interaction.Comment: 18 pages, 13 figures, 1 table, submitted to Ap

Comoving stars in the Gaia era

Comoving stars range from wide binaries to dense open clusters, and provide a unique window into the Milky Way. They are consequences of recent star formation which occurs highly clustered in giant molecular clouds, and the stellar and dynamical evolution that follows. Recent data releases from the Gaia astrometric mission together with the on-going large spectroscopic surveys provide an ideal playground to study the entire spectrum of comoving stars and illuminate the formation and disruption of these objects. This thesis contains a series of projects related to finding and characterizing comoving stars with the Gaia data. After a brief general introduction in Chapter 1, I develop a method to search for comoving pairs of stars using astrometric data based on a probabilistic model selection in Chapter 2. I apply the method to the first data release of the Gaia mission and find 13,085 pairs among 10,606 stars, which make up 4,555 comoving systems. I follow up two of these systems in detail. In Chapter 3, I study the metallicity and abundance differences of a wide binary, HD 240429 and HD 240430. I discuss the possible reasons for the significant and condensation temperature-dependent abundance differences between the two stars and argue that one of the stars has likely accreted a massive, rocky planetary system. In Chapter 4, I confirm and characterize the nearest and largest new comoving group discovered in Chapter 2, using the second data release of Gaia. I extend the candidate members and discuss its morphology in relation to its disruption