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NGC5457 
Date 30.05.15 


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NGC 5457
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Messier 101 (also M101, The Pinwheel Galaxy, NGC 5457, UGC 8981 and PGC 50063) is a magnitude +7.9 face-on spiral galaxy located 20.9 ±1.8 million light-years away in the constellation Ursa Major. 

The galaxy was discovered by French astronomer Pierre Méchain using a 15.24 cm (6 inch) reflector on the 27th March 1781.
The galaxy was observed by Charles Messier and listed as M102.

Right Ascension 4h 03m 12.6s, Declination +54° 20' 57" 

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Pinwheel spiral galaxy
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The Pinwheel Galaxy, by ESA's XMM-Newton space telescope

The face-on Pinwheel spiral galaxy is seen at ultraviolet wavelengths in this image taken by ESA's XMM-Newton space telescope.
Also known as M101, the galaxy lies 21 million light-years away in the constellation Ursa Major. It measures 170 000 light-years across - nearly twice the diameter of our own Milky Way Galaxy - and contains at least a trillion stars. About a billion of these stars could be similar to our own Sun.

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H 1013
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Title: No temperature fluctuations in the giant HII region H 1013
Authors: G. Stasinska, C. Morisset, S. Simon-Diaz, F. Bresolin, D. Schaerer, B. Brandl

While collisionally excited lines in HII regions allow one to easily probe the chemical composition of the interstellar medium in galaxies, the possible presence of important temperature fluctuations casts some doubt on the derived abundances. To provide new insights into this question, we have carried out a detailed study of a giant HII region, H 1013, located in the galaxy M101, for which many observational data exist and which has been claimed to harbour temperature fluctuations at a level of t^2 = 0.03-0.06. We have first complemented the already available optical observational datasets with a mid-infrared spectrum obtained with the Spitzer Space Telescope. Combined with optical data, this spectrum provides unprecedented information on the temperature structure of this giant HII region. A preliminary analysis based on empirical temperature diagnostics suggests that temperature fluctuations should be quite weak. We have then performed a detailed modelling using the pyCloudy package based on the photoionisation code Cloudy. We have been able to produce photoionisation models constrained by the observed Hb surface brightness distribution and by the known properties of the ionising stellar population than can account for most of the line ratios within their uncertainties. Since the observational constraints are both strong and numerous, this argues against the presence of significant temperature fluctuations in H 1013. The oxygen abundance of our best model is 12 + log O/H = 8.57, as opposed to the values of 8.73 and 8.93 advocated by Esteban et al. (2009) and Bresolin (2007), respectively, based on the significant temperature fluctuations they derived. However, our model is not able to reproduce the intensities of the oxygen recombination lines . This cannot be attributed to observational uncertainties and requires an explanation other than temperature fluctuations.

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Title: The Extended Optical Disk of M101
Authors: Chris Mihos, Paul Harding, Chelsea Spengler, Craig Rudick, John Feldmeier

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 M101's 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 colours (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 M101's 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 M101's outer disk due to encounters in the group environment triggering extended star formation and tidal heating of existing disk populations.

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M101 group
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Title: The HI environment of the M101 group
Authors: Chris Mihos, Katie Keating, Kelly Holley-Bockelmann, D. J. Pisano, Namir Kassim

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 M101's 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 solar masses 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 solar masses, 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.

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 A Pinwheel in Many Colours

m101_w1.jpg

This image of the Pinwheel Galaxy, or also known as M101, combines data in the infrared, visible, ultraviolet and X-rays from four of NASA's space-based telescopes. This multi-spectral view shows that both young and old stars are evenly distributed along M101's tightly-wound spiral arms. Such composite images allow astronomers to see how features in one part of the spectrum match up with those seen in other parts. It is like seeing with a regular camera, an ultraviolet camera, night-vision goggles and X-ray vision, all at the same time.
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Title: Physical Structure and Nature of Supernova Remnants in M101
Authors: N. A. Franchetti (1), R. A. Gruendl (1), Y.-H. Chu (1), B. C. Dunne (1), T. G. Pannuti (2), K. D. Kuntz (3), C.-H. R. Chen (4,5), C. K. Grimes (2), T. M. Aldridge (6) ((1) University of Illinois, (2) Morehead State University, (3) Johns Hopkins University,(4) University of Virginia, (5) MPIfR, (6) Northern Illinois University)

Supernova remnant (SNR) candidates in the giant spiral galaxy M101 have been previously identified from ground-based H-alpha and [SII] images. We have used archival Hubble Space Telescope (HST) H-alpha and broad-band images as well as stellar photometry of 55 SNR candidates to examine their physical structure, interstellar environment, and underlying stellar population. We have also obtained high-dispersion echelle spectra to search for shocked high-velocity gas in 18 SNR candidates, and identified X-ray counterparts to SNR candidates using data from archival observations made by the Chandra X-ray Observatory. Twenty-one of these 55 SNR candidates studied have X-ray counterparts, although one of them is a known ultra-luminous X-ray source. The multi-wavelength information has been used to assess the nature of each SNR candidate. We find that within this limited sample, ~16% are likely remnants of Type Ia SNe and ~45% are remnants of core-collapse SNe. In addition, about ~36% are large candidates which we suggest are either superbubbles or OB/HII complexes. Existing radio observations are not sensitive enough to detect the non-thermal emission from these SNR candidates. Several radio sources are coincident with X-ray sources, but they are associated with either giant HII regions in M101 or background galaxies. The archival HST H-alpha images do not cover the entire galaxy and thus prevents a complete study of M101. Furthermore, the lack of HST [SII] images precludes searches for small SNR candidates which could not be identified by ground-based observations. Such high-resolution images are needed in order to obtain a complete census of SNRs in M101 for a comprehensive investigation of the distribution, population, and rates of SNe in this galaxy.

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M101 Cepheids
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Title: A New Cepheid Distance to the Giant Spiral M101 Based On Image Subtraction of HST/ACS Observations
Authors: Benjamin J. Shappee, K. Z. Stanek

We accurately determine a new Cepheid distance to M101 (NGC 5457) using archival HST/ACS V and I time series photometry of two fields within the galaxy. We make a slight modification to the ISIS image subtraction package to obtain optimal differential light curves from HST data. We discovered 827 Cepheids with periods between 3 and 80 days, the largest extragalactic sample of Cepheids observed with HST by a factor of 2. With this large Cepheid sample we find that the relative distance of M101 from the LMC is delta {\mu}LMC = 10.63 ±0.04 (random) ±0.07 (systematic) mag. If we use the geometrically determined maser distance to NGC 4258 as our distance anchor, the distance modulus of M101 is {\mu}0 = 29.04 ±0.05 (random) ±0.18 (systematic) mag or D = 6.4 ±0.2 (random) ±0.5 (systematic) Mpc. The uncertainty is dominated by the maser distance estimate (±0.15 mag), which should improve over the next few years. We determine a steep metallicity dependence, gamma, for our Cepheid sample through two methods, yielding gamma = -0.84 ±0.22 (random) ±0.07 (systematic) mag dex-1 and gamma = -0.72+0.20 -0.22 (random) ±0.06 (systematic) mag dex-1. We see marginal evidence for variations in the Wesenheit P-L relation slope as a function of deprojected galactocentric radius. We also use the TRGB method to independently determine the distance modulus to M101 of {\mu}0 = 29.05 ±0.06 (random) ±0.12 (systematic) mag.

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The Isaac Newton Telescope captures the Full Monty
The Pinwheel Galaxy is one of the most fantastic spiral galaxies to view because it faces the Earth, showing itself in all its awesome glory.

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