Galaxy formation and evolution

Abstract:

A new, 2.8 deg2 J, H, Ks near-infrared (MR) survey from the 2MASS 6X program across the extent of the optical disk of the Andromeda (M31) galaxy provides a clear view of the M31 center almost completely unfettered by dust extinction and reveals a high-contrast bulge with very boxy isophotes dominating the NIR light to a semimajor axis of ∼700" (2.6 kpc). The inner bulge (≲50") isophotes are relatively circular but show some twisting. Beyond this, (1) the M31 bulge ellipticity increases, (2) its position angle is constant at ∼50°, or about 10° higher than the position angle of the M31 disk, and (3) its boxiness increases to a degree (∼3%-4%) comparable to other renowned examples of boxy bulges observed in the NIR. In a companion paper, self-consistent N-body simulations of a classical bulge plus a bar with a boxy bulge are shown to reproduce the observed NIR M31 features presented here. Beyond the boxy bulge region and nearly along the 40° position angle of the disk a narrow ridge of NIR flux, which can be identified with the thin part of the bar, more or less symmetrically extends into the inner disk at semimajor axis radii of 700"-1200" or more. Little variation in the morphology or relative brightnesses of these various M31 structures is seen across the NIR bands (e.g., no color gradients are seen). These new data verify that M31 is a barred spiral galaxy like the Milky Way. © 2007. The American Astronomical Society. All rights reserved.

Abstract:

We present new photometric and spectroscopic measurements for the unique, young, low-mass evolutionary track calibrator AB Dor C. While the new Ks photometry is similar to that previously published in Close et al. (2005) the spectral type is found to be earlier. Based on new H & K IFS spectra of AB Dor C (Thatte et al. 2007; paper 1) we adopt a spectral type of M5.5+/-1.0 for AB Dor C. This is considerably earlier than the M8+/-1 estimated in Close et al. (2005) and Nielsen et al. (2005) yet is consistent with the M6+/-1 independently derived by Luhman & Potter (2005). However, the spectrum presented in paper 1 and analyzed here is a significant improvement over any previous spectrum of AB Dor C. We also present new astrometry for the system which further supports a 0.090+/-0.005 Msun mass for the system. Once armed with an accurate spectrum and Ks flux we find L=0.0021+/-0.0005 Lsun and Teff=2925{+170}{-145}K for AB Dor C. These values are consistent with a ~75 Myr 0.090+/-0.005 Msun object like AB Dor C according to the DUSTY evolutionary tracks (Chabrier et al. 2000). Hence masses can be estimated from the HR diagram with the DUSTY tracks for young low-mass objects like AB Dor C. However, we cautiously note that underestimates of the mass from the tracks can occur if one lacks a proper (continuum preserved) spectra or is relying on NIR fluxes alone.