As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) we report the discovery of a pair of faint dwarf galaxies (CenA-MM-Dw1 and CenA-MM-Dw2) at a projected distance of $sim$90 kpc from the nearby elliptical galaxy NGC5128 (CenA)
. We measure a tip of the red giant branch distance to each dwarf, finding $D=3.63 pm 0.41$ Mpc for CenA-MM-Dw1 and $D=3.60 pm 0.41$ Mpc for CenA-MM-Dw2, both of which are consistent with the distance to NGC5128. A qualitative analysis of the color magnitude diagrams indicates stellar populations consisting of an old, metal-poor red giant branch ($gtrsim 12$ Gyr, [Fe/H]$sim-1.7$ to -1.9). In addition, CenA-MM-Dw1 seems to host an intermediate-age population as indicated by its candidate asymptotic giant branch stars. The derived luminosities ($M_V=-10.9pm0.3$ for CenA-MM-Dw1 and $-8.4pm0.6$ for CenA-MM-Dw2) and half-light radii ($r_{h}=1.4pm0.04$ kpc for CenA-MM-Dw1 and $0.36pm0.08$ kpc for CenA-MM-Dw2) are consistent with those of Local Group dwarfs. CenA-MM-Dw1s low central surface brightness ($mu_{V,0}=27.3pm0.1$ mag/arcsec$^2$) places it among the faintest and most extended M31 satellites. Most intriguingly, CenA-MM-Dw1 and CenA-MM-Dw2 have a projected separation of only 3 arcmin ($sim3$ kpc): we are possibly observing the first, faint satellite of a satellite in an external group of galaxies.
We analyze our accurate kinematical data for the old clusters in the inner regions of M31. These velocities are based on high S/N Hectospec data (Caldwell et al 2010). The data are well suited for analysis of M31s inner regions because we took partic
ular care to correct for contamination by unresolved field stars from the disk and bulge in the fibers. The metal poor clusters show kinematics which are compatible with a pressure-supported spheroid. The kinematics of metal-rich clusters, however, argue for a disk population. In particular the innermost region (inside 2 kpc) shows the kinematics of the x2 family of bar periodic orbits, arguing for the existence of an inner Lindblad resonance in M31.
We report on a single star, B030D, observed as part of a large survey of objects in M31, which has the unusual radial velocity of -780 km/s. Based on details of its spectrum, we find that the star is an F supergiant, with a circumstellar shell. The e
volutionary status of the star could be one of a post-mainsequence close binary, a symbiotic nova, or less likely, a post-AGB star, which additional observations could help sort out. Membership of the star in the Andromeda Giant Stream can explain its highly negative velocity.
We have obtained optical spectra of 29 early-type (E/S0) galaxies that hosted type Ia supernovae (SNe Ia). We have measured absorption-line strengths and compared them to a grid of models to extract the relations between the supernova properties and
the luminosity-weighted age/composition of the host galaxies. The same analysis was applied to a large number of early-type field galaxies selected from the SDSS spectroscopic survey. We find no difference in the age and abundance distributions between the field galaxies and the SN Ia host galaxies. We do find a strong correlation suggesting that SNe Ia in galaxies whose populations have a characteristic age greater than 5 Gyr are ~ 1 mag fainter at V(max) than those found in galaxies with younger populations. However, the data cannot discriminate between a smooth relation connecting age and supernova luminosity or two populations of SN Ia progenitors. We find that SN Ia distance residuals in the Hubble diagram are correlated with host-galaxy metal abundance, consistent with the predictions of Timmes, Brown & Truran (2003). The data show that high iron abundance galaxies host less-luminous supernovae. We thus conclude that the time since progenitor formation primarily determines the radioactive Ni production while progenitor metal abundance has a weaker influence on peak luminosity, but one not fully corrected by light-curve shape and color fitters. Assuming no selection effects in discovering SNe Ia in local early-type galaxies, we find a higher specific SN Ia rate in E/S0 galaxies with ages below 3 Gyr than in older hosts. The higher rate and brighter luminosities seen in the youngest E/S0 hosts may be a result of recent star formation and represents a tail of the prompt SN Ia progenitors.
A SST survey in the NOAO Deep-Wide Field in Bootes provides a complete, 8-micron-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg$^2$ field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an
accurate determination of the local (z<0.3) galaxy luminosity function. Stellar and dust emission can be separated on the basis of observed galaxy colors. Dust emission (mostly PAH) accounts for 80% of the 8 micron luminosity, stellar photospheres account for 19%, and AGN emission accounts for roughly 1 %. A sub-sample of the 8 micron-selected galaxies have blue, early-type colors, but even most of these have significant PAH emission. The luminosity functions for the total 8 micron luminosity and for the dust emission alone are both well fit by Schechter functions. For the 8 micron luminosity function, the characteristic luminosity is u L_{ u}^*(8.0 micron) = 1.8 times 10^{10}$ Lsun while for the dust emission alone it is 1.6 x 10^{10}$ Lsun ull. The average 8 micron luminosity density at z<0.3 is 3.1 x 10^7 Lsun Mpc^{-3}, and the average luminosity density from dust alone is 2.5 x 10^7 Lsun Mpc^{-3}. This luminos ity arises predominantly from galaxies with 8 micron luminosities ($ u L_{ u}$) between $2times 10^9$ and $2 x 10^{10}$ Lsun, i.e., normal galaxies, not LIRGs or ULIRGs.
