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RE: Messier 74
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Title: NGC628 with SITELLE : I. Imaging Spectroscopy of 4285 HII region candidates
Author: Laurie Rousseau-Nepton, Carmelle Robert, Laurent Drissen, R. Pierre Martin, Thomas Martin

This is the first paper of a series dedicated to nebular physics and the chemical evolution of nearby galaxies by investigating large samples of HII regions with the CFHT imaging spectrograph SITELLE. We present a technique adapted to imaging spectroscopy to identify and extract parameters from 4285 HII region candidates found in the disc of NGC 628. Using both the spatial and spectral capabilities of SITELLE, our technique enables the extraction of the position, dust extinction, velocity, H alpha profile, diffuse ionized gas (DIG) background, luminosity, size, morphological type, and the emission line fluxes for individual spaxels and the integrated spectrum for each region. We have produced a well-sampled HII region luminosity function and studied its variation with galactocentric radius and level of the DIG background. We found a slope alpha of -1.12±0.03 with no evidence of a break at high luminosity. Based on the width of the region profile, bright regions are rather compact, while faint regions are seen over a wide range of sizes. The radius function reveals a slope of -1.81±0.02. BPT diagrams of the individual spaxels and integrated line ratios confirm that most detections are HII regions. Also, maps of the line ratios show complex variations of the ionization conditions within HII regions. All this information is compiled in a new catalog for HII regions. The objective of this database is to provide a complete sample which will be used to study the whole parameter space covered by the physical conditions in active star-forming regions.

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Title: A revised planetary nebula luminosity function distance to NGC 628 using MUSE
Author: K. Kreckel, B. Groves, F. Bigiel, G. Blanc, J. M. D. Kruijssen, A. Hughes, A. Schruba, E. Schinnerer

Distance uncertainties plague our understanding of the physical scales relevant to the physics of star formation in extragalactic studies. The planetary nebulae luminosity function (PNLF) is one of very few techniques that can provide distance estimates to within ~10%, however it requires a planetary nebula (PN) sample that is uncontaminated by other ionizing sources. We employ optical IFU spectroscopy using MUSE on the VLT to measure [OIII] line fluxes for sources unresolved on 50 pc scales within the central star-forming galaxy disk of NGC 628. We use diagnostic line ratios to identify 62 PNe, 30 supernova remnants and 87 HII regions within our fields. Using the 36 brightest PNe we determine a new PNLF distance modulus of 29.91^{+0.08}_{-0.13} mag (9.59^{+0.35}_{-0.57} Mpc), in good agreement with literature values but significantly larger than the previously reported PNLF distance. We are able to explain the discrepancy and recover the previous result when we reintroduce SNR contaminants to our sample. This demonstrates the power of full spectral information over narrowband imaging in isolating PNe. Given our limited spatial coverage within the galaxy, we show that this technique can be used to refine distance estimates even when IFU observations cover only a fraction of a galaxy disk.

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Messier 74 (also M74, NGC 628, IRAS 01340+1532, MCG 3-5-11, UGC 1149 and PGC 5974) is a magnitude +10.0 face-on spiral galaxy located 30 ±6 million light-years away in the constellation Pisces. 
The galaxy was discovered by French astronomer Pierre Francois Andre Mechain using a 15.24 cm (6 inch) speculum newtonian reflector in late September 1780
Charles Messier also observed the galaxy and included it in his catalogue on the 18th October 1780.

Position (J2000): R.A. 01h 36m 41.8s  |  Dec. +15° 47' 01"

The galaxy's low surface brightness makes it the most difficult Messier object for amateur astronomers to observe.
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Phantom Galaxy Revealed
 


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NGC 628
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M74 Image Overlay.kmz
Google Sky file (1kb, kmz)



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Messier 74
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Resembling festive lights on a holiday wreath, this NASA/ESA Hubble Space Telescope image of the nearby spiral galaxy M74 is an iconic reminder of the impending season. Bright knots of glowing gas light up the spiral arms, indicating a rich environment of star formation. M74 is located roughly 32 million light-years away in the direction of the constellation Pisces, the Fish. The image is a composite of Advanced Camera for Surveys data taken in 2003 and 2005.

web.jpg
Messier 74, also called NGC 628, is a stunning example of a "grand-design" spiral galaxy that is viewed by Earth observers nearly face-on.
Credit: NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration

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Title: HI power spectrum of the spiral galaxy NGC628
Authors: Prasun Dutta (IIT, KGP), Ayesha Begum (IoA, Cambridge), Somnath Bharadwaj (IIT, KGP), Jayaram N. Chengalur (NCRA, TIFR)

We have measured the HI power spectrum of the nearly face-on spiral galaxy NGC628 (M74) using a visibility based estimator. The power spectrum is well fitted by a power law P(U)=AU^{\alpha}, with \alpha =- 1.6 ±0.2 over the length scale 800 pc to 8 kpc. The slope is found to be independent of the width of the velocity channel. This value of the slope is a little more than one in excess of what has been seen at considerably smaller length scales in the Milky-Way, Small Magellanic Cloud (LMC), Large Magellanic Cloud (SMC) and the dwarf galaxy DDO210. We interpret this difference as indicating a transition from three dimensional turbulence at small scales to two dimensional turbulence in the plane of the galaxy's disk at length scales larger than galaxy's HI scale height.
The slope measured here is similar to that found at large scales in the LMC. Our analysis also places an upper limit to the galaxy's scale height at 800 pc .

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