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Register a new userThe Extended Optical Disk of M101
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We have used deep, wide-field optical imaging to study the faint outskirts of the luminous spiral galaxy M101 (NGC 5457), as well as its surrounding environment. Over six square degrees, our imaging has a limiting surface brightness of mu_B ~ 29.5 mag/arcsec^2, and has revealed the stellar structure of M101s disk out to nearly 25 arcminutes (50 kpc), three times our measured R25 isophotal size of the optical disk. At these radii, the well-known asymmetry of the inner disk slews 180 degrees, resulting in an asymmetric plume of light at large radius which follows the very extended HI disk to the northeast of M101. This plume has very blue colors (B-V ~ 0.2), suggesting it is the somewhat more evolved (few hundred Myr to ~ 1 Gyr) counterpart of the young far ultraviolet emitting population traced by GALEX imaging. We also detect another, redder spur of extended light to the east of the disk, and both structures are reminiscent of features produced during fly-by galaxy interactions. However, we see no evidence of very extended tidal tails around M101 or any of its companions which might be expected from a recent encounter with a massive companion. We consider the properties of M101s outer disk in light of possible past interactions with the nearby companion galaxies NGC 5477 and NGC 5474. The detection of optical starlight at such large radii gives us the ability to study star formation histories and stellar populations in outer disks over a longer timescales than those traced by the UV or Halpha emitting populations. Our data suggest ongoing buildup of the M101s outer disk due to encounters in the group environment triggering extended star formation and tidal heating of existing disk populations.
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We present near infra-red light curves of supernova (SN) 2011fe in M101, including 34 epochs in H band starting fourteen days before maximum brightness in the B-band. The light curve data were obtained with the WIYN High-Resolution Infrared Camera (WHIRC). When the data are calibrated using templates of other Type Ia SNe, we derive an apparent H-band magnitude at the epoch of B-band maximum of 10.85 pm 0.04. This implies a distance modulus for M101 that ranges from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia SNe is used.
We present a wide (8.5x6.7 degree, 1050x825 kpc), deep (sigma(N_HI)=10^(16.8-17.5) cm^-2) neutral hydrogen (HI) map of the M101 galaxy group. We identify two new HI sources in the group environment, one an extremely low surface brightness (and hitherto unknown) dwarf galaxy, and the other a starless HI cloud, possibly primordial in origin. Our data show that M101s extended HI envelope (Huchtmeier & Witzel 1979) takes the form of a ~100 kpc long tidal loop or plume of HI extending to the southwest of the galaxy. The plume has an HI mass ~ 10^8 Msun and a peak column density of N_HI=5x10^17 cm^-2, and while it rotates with the main body of M101, it shows kinematic peculiarities suggestive of a warp or flaring out of the rotation plane of the galaxy. We also find two new HI clouds near the plume with masses ~ 10^7 Msun, similar to HI clouds seen in the M81/M82 group, and likely also tidal in nature. Comparing to deep optical imaging of the M101 group, neither the plume nor the clouds have any extended optical counterparts down to a limiting surface brightness of mu_B = 29.5. We also trace HI at intermediate velocities between M101 and NGC 5474, strengthening the case for a recent interaction between the two galaxies. The kinematically complex HI structure in the M101 group, coupled with the optical morphology of M101 and its companions, suggests that the group is in a dynamically active state that is likely common for galaxies in group environments.
We present $ugR$ optical images taken with the MMT/Megacam and the Subaru/Suprime of the Extended Groth Strip survey. The total survey covers an area of about $sim 1$ degree$^2$, including four sub-fields and is optimized for the study of galaxies at $zsim3$. Our methods for photometric calibration in AB magnitudes, the limiting magnitude and the galaxy number count are described. A sample of 1642 photometrically selected candidate LBGs to an apparent $R_{AB}$ magnitude limit of 25.0 is present. The average sky surface density of our LBGs sample is $sim$ 1.0 arcmin$^{-2}$, slightly higher than the previous finding.
We use deep Hubble Space Telescope imaging in the outskirts of the nearby spiral M101 to study stellar populations in the galaxys outer disk and halo. Our ACS field lies 17.6 arcmin (36 kpc) from the center of M101 and targets the blue NE Plume of M101s outer disk, while the parallel WFC3 field lies at a distance of 23.3 arcmin (47 kpc) to sample the galaxys stellar halo. The WFC3 halo field shows a well-defined red giant branch characterized by low metallicity ([M/H]=-1.7 $pm$ 0.2), with no evidence of young stellar populations. In contrast, the ACS disk field shows multiple stellar populations, including a young main sequence, blue and red helium burning stars, and old RGB and AGB populations. The mean metallicity of these disk stars is quite low: [M/H]=-1.3 $pm$ 0.2 for the RGB population, and -1.15 $pm$ 0.2 for the younger helium burning sequences. Of particular interest is a bunching of stars along the BHeB sequence, indicative of an evolving cohort of massive young stars. We show that the young stellar populations in this field are well-described by a decaying burst of star formation that peaked ~ 300-400 Myr ago, along with a more extended star formation history to produce the older RGB and AGB populations. These results confirm and extend the results from our previous deep surface photometry of M101s outer disk, providing an important cross-check on stellar population studies using resolved stellar populations versus integrated light photometry. We discuss our results in the context of halo formation models and the interaction history of M101 and its companions.
We have identified a few thousand star clusters in the nearby, late-type spiral galaxy M101, including approximately 90 candidate ancient globular clusters (GCs), from multi-band Hubble Space Telescope (HST) images. We obtained follow-up low-resolution (R approximately 2000) optical spectroscopy from Gemini-GMOS for 43 total clusters, of which 18 are old GCs and 25 are young massive clusters (YMCs). We measure radial velocities for these clusters and find that, as expected, the YMCs rotate with the HI disk. The old GCs do not show any obvious evidence for rotation and have a much higher velocity dispersion than the YMCs, suggesting that the GCs in M101 are likely part of a stellar halo or thick disk.
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