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 present 7 spectroscopically confirmed Type II cluster supernovae (SNeII) discovered in the Multi-Epoch Nearby Cluster Survey, a supernova survey targeting 57 low redshift 0.05 < z < 0.15 galaxy clusters with the Canada-France-Hawaii Telescope. We
find the rate of Type II supernovae within the virial radius of these galaxy clusters to be 0.026 (+0.085 -0.018 stat; +0.003 -0.001 sys) SNe per century per 1e10 solar masses. Surprisingly, one SNII is in a red sequence host galaxy that shows no clear evidence of recent star formation. This is unambiguous evidence in support of ongoing, low-level star formation in at least some cluster elliptical galaxies, and illustrates that galaxies that appear to be quiescent cannot be assumed to host only Type Ia SNe. Based on this single SNII we make the first measurement of the SNII rate in red sequence galaxies, and find it to be 0.007 (+0.014 -0.007 stat; +0.009 -0.001 sys) SNe per century per 1e10 solar masses. We also make the first derivation of cluster specific star formation rates (sSFR) from cluster SNII rates. We find that for all galaxy types, sSFR is 5.1 (+15.8 -3.1 stat; +0.9 -0.9 sys) solar masses per year per 1e12 solar masses, and for red sequence galaxies only, it is 2.0 (+4.2 -0.9 stat; +0.4 -0.4 sys) solar masses per year per 1e12 solar masses. These values agree with SFRs measured from infrared and ultraviolet photometry, and H-alpha emission from optical spectroscopy. Additionally, we use the SFR derived from our SNII rate to show that although a small fraction of cluster Type Ia SNe may originate in the young stellar population and experience a short delay time, these results do not preclude the use of cluster SNIa rates to derive the late-time delay time distribution for SNeIa.
We present deep wide-field photometry of three recently discovered faint Milky Way satellites: Leo V, Pisces II, and Canes Venatici II. Our main goals are to study the structure and star formation history of these dwarfs; we also search for signs of
tidal disturbance. The three satellites have similar half-light radii ($sim 60-90$ pc) but a wide range of ellipticities. Both Leo V and CVn II show hints of stream-like overdensities at large radii. An analysis of the satellite color-magnitude diagrams shows that all three objects are old ($>$ 10 Gyr) and metal-poor ([Fe/H] $sim -2$), though neither the models nor the data have sufficient precision to assess when the satellites formed with respect to cosmic reionization. The lack of an observed younger stellar population ($la 10$ Gyr) possibly sets them apart from the other satellites at Galactocentric distances $ga 150$ kpc. We present a new compilation of structural data for all Milky Way satellite galaxies and use it to compare the properties of classical dwarfs to the ultra-faints. The ellipticity distribution of the two groups is consistent at the $sim$2-$sigma$ level. However, the faintest satellites tend to be more aligned toward the Galactic center, and those satellites with the highest ellipticity ($ga 0.4$) have orientations ($Delta theta_{GC}$) in the range $20^{circ} lesssim Delta theta_{GC} lesssim 40^{circ}$. This latter observation is in rough agreement with predictions from simulations of dwarf galaxies that have lost a significant fraction of their dark matter halos and are being tidally stripped.
