Local Group Spiral Galaxy Research Articles

Deep XMM‐Newton survey of M33

AbstractIn an XMM‐Newton raster observation of the bright local group spiral galaxy M33 we study the population of X‐ray sources (X‐ray binaries, supernova remnants, super‐shells) down to a 0.5–10 keV luminosity of 1035 erg s–1 – more than a factor of 10 deeper than earlier ROSAT observations. EPIC spectra and hardness ratios are used to distinguish between different source classes.We confirmed the 3.45 d orbital light curve of the X‐ray binaryM33 X7, detected a transient super‐soft source in M33, and searched for short term variability of the brighter sources. We characterize the diffuse X‐ray component that is correlated with the inner disk and spiral arms. We will compare the results with other nearby galaxies.

The Formation Chronology of Local Group Spiral Galaxies

The ‘Second Parameter Effect’ (2ndPE) has long been recognized as an important probe into the formation of spiral galaxies. The concept that the horizontal branch morphologies of globular clusters are primarily affected by metal abundance in the inner halo (RGC<8 kpc) of the Galaxy but require an additional parameter (probably cluster age) to explain their behavior in the outer halo (RGC > 8 kpc), suggests that the former experienced a rapid monotonic collapse while the latter underwent a slower chaotic formation scenario. As such, in the Milky Way, the so-called second parameter boundary is located at 8 kpc. We find that, in the other Local Group spirals — M31 and M33 — this boundary lies at ∼40 kpc and ∼0 kpc, respectively. We therefore speculate that the boundary delimiting rapid monotonic halo collapse from the chaotic accretion of dwarf galaxy fragments is inversely related to the mass of the spiral galaxy.

An X-Ray Emitting Supernova Remnant Candidate, M 33 X-4

Abstract Based on ASCA observations of the Local-Group spiral galaxy M 33, a report is made on the X-ray properties of luminous X-ray source called X-4, which is located in a giant H ii region in M 33. The 0.8-8.0keV spectrum of X-4 is described by a two-component model, consisting of a thin thermal plasma emission with a temperature of $ \sim 1.0 \,\mathrm{keV}$, and a power law emission with a photon index of $ \sim 2.0$. The two spectral components cross over at $ \sim 3.0 \,\mathrm{keV}$. These spectral properties are similar to those of a young supernova remnant (SNR), except that the 0.8-8.0keV luminosity of M 33 X-4, $ \sim 1.0 \times 10^{38} \,\mathrm{erg} \,\mathrm{s}^{-1}$, is considerably higher than those of the SNRs in the Milky Way. There is also evidence of excess absorption, or an over-abundance of $ \alpha$-elements relative to iron. If this source is an SNR, the hard component is thought to be synchrotron radiation from high-energy particles, produced either by shock acceleration, like in SN 1006, or by a central neutron star, like in the Crab Nebula.

The X-ray view of M 33 after ROSAT

We present a catalogue of 184 X-ray sources within 50 0 of the nucleus of the local group spiral galaxy M 33. The catalogue is derived from an analysis of the complete set of ROSAT archival data pointed in the direction of M 33 and contains X-ray position, existence likelihood, count rates and PSPC spectral hardness ratios. To identify the sources the catalog was correlated with previous X-ray catalogues, optical and radio catalogues. In addition sources were classied according to their X-ray properties. We nd seven candidates for supersoft X-ray sources, of which two may be associated with known planetary nebulae in M 33. The majority of X-ray detected supernova remnants is also detected at radio frequencies and seen in optical lines. The low overall X-ray detection rate of optically selected SNRs can probably be attributed to their expansion into interstellar matter of low density.

Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby S[CLC]c[/CLC] Galaxies. I. M33

Near-infrared images obtained with the Canada-France-Hawaii Telescope (CFHT) Adaptive Optics Bonnette (AOB) are used to investigate the stellar content within 18 arcsec of the center of the Local Group spiral galaxy M33. AGB stars with near-infrared spectral-energy distributions similar to those of giants in the solar neighborhood and Baade's Window are detected over most of the field. The bolometric luminosity function (LF) of these stars has a discontinuity near M_{bol} = -5.25, and comparisons with evolutionary tracks suggest that most of the AGB stars formed in a burst of star formation 1 - 3 Gyr in the past. The images are also used to investigate the integrated near-infrared photometric properties of the nucleus and the central light concentration. The nucleus is bluer than the central light concentration, in agreement with previous studies at visible wavelengths. The CO index of the central light concentration 0.5 arcsec from the galaxy center is 0.05, which corresponds to [Fe/H] = -1.2 for simple stellar systems. Hence, the central light concentration could not have formed from the chemically-enriched material that dominates the present-day inner disk of M33.

The Density and Temperature of Molecular Clouds in M33

We have observed the 12CO J = 2-1,13CO J = 2-1, and 12CO J = 3-2 lines in a sample of seven giant molecular clouds in the Local Group spiral galaxy M33 using the James Clerk Maxwell Telescope. The 12CO/13CO J = 2-1 line ratio is constant across the entire sample, while the observed 12CO J = 3-2/J = 2-1 line ratio has a weak dependence on the star formation environment of the cloud, with large changes in the line ratio seen only for clouds in the immediate vicinity of an extremely luminous H II region. A large velocity gradient analysis indicates that clouds without H II regions have temperatures of 10-20 K, clouds with H II regions have temperatures of 15-100 K, and the cloud in the giant H II region has a temperature of at least 100 K. Interestingly, the giant H II region appears capable of raising the kinetic temperature of the molecular gas only for clouds that are quite nearby (<100 pc). The continuous change of physical conditions across the observed range of star formation environments suggests that the unusual physical conditions in the cloud in the giant H II region are due to post-star formation changes in the molecular gas, rather than intrinsic properties of the gas related to the formation of the giant H II region. The results from this study of M33 suggest that similar observations of ensembles of giant molecular clouds in more distant normal spiral galaxies are likely to give meaningful measurements of the average physical conditions inside the molecular clouds. These results also imply that clouds with a factor of 3 difference in metallicity have similar density and temperature, which in turn implies that the differences in the CO-to-H2 conversion factor seen in these clouds can be attributed to metallicity effects entirely.

First observations of individual molecular clouds in the irregular galaxy NGC 6822

view Abstract Citations (37) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS First Observations of Individual Molecular Clouds in the Irregular Galaxy NGC 6822 Wilson, Christine D. Abstract Three molecular clouds have been mapped in the nearby metal-poor dwarf irregular galaxy NGC 6822 using the Owens Valley Millimeter-Wave Interferometer. These molecular clouds are similar to molecular clouds recently studied in the Small Magellanic Cloud, and are somewhat less massive on average than molecular clouds in Local Group spiral galaxies. Based on upper limits to the virial masses of the clouds, the CO-to-H_2_ conversion factor in NGC 6822 is < 2.2 +/- 1.3 times larger than the Galactic value [3 x 10^20^ cm^-2^ (K km s^-1^)^-1^]. Conversion factors obtained for Galactic molecular clouds, NGC 6822, and the SMC are consistent with the variation in the CO-to-H_2_ conversion factor being linearly proportional to the oxygen abundance of the galaxy. However, the uncertainties are sufficiently large that equal conversion factors in NGC 6822 and the Galaxy cannot be ruled out. The gas depletion time obtained for the H II region Hubble V is comparable to those of giant H II regions in M33. Thus high-efficiency star formation is not limited to the giant H II regions seen spiral galaxies, but can also occur in a small group of relatively low-mass (a few times 10^4^ M_sun_) molecular clouds. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/187560 arXiv: arXiv:astro-ph/9407070 Bibcode: 1994ApJ...434L..11W Keywords: Abundance; Irregular Galaxies; Local Group (Astronomy); Molecular Clouds; Astronomical Interferometry; Brightness Temperature; Galactic Mass; Oxygen; Star Formation; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 6822; GALAXIES: IRREGULAR; GALAXIES: ISM; GALAXIES: LOCAL GROUP; ISM: MOLECULES; Astrophysics E-Print: 8 pages + 5 figures, uuencoded compressed postscript file, CDW-94-2 full text sources arXiv | ADS | data products SIMBAD (8) NED (1)

Deciphering a Rosetta Stone - The nebula MA 1 in M33

We present a new longslit CCD spectrum and Hα imaging of the nebula MA 1 in the Local Group spiral galaxy M33, one of McCall's four «Rosetta Stone» extragalactic H II regions. Our Hα image shows MA 1 to be a complex of arcs, loops, and filaments having a diameter of about 45 arcsec. Our spectrum does not confirm McCall's suggestion that MA 1 is a matter-bounded nebula; rather, the spatial profile of the emission lines shows that [O II] is quite weak near the central stellar object, but becomes more nearly normal in strength in the outer parts of the nebula

OB associations in the inner two kiloparsecs of M33

view Abstract Citations (60) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS OB Associations in the Inner Two Kiloparsecs of M33 Wilson, Christine D. Abstract UBV CCD photometry for the inner 7X10^arcmin^ of the Local Group spiral galaxy M33 is used to identify the OB associations and to study their properties. The association boundaries are identified using a "friends of friends" grouping algorithm, in which the major remaining source of subjectivity is the search radius chosen. We find 41 associations in this region of M33, each containing at least ten blue stars. These associations have mean radii of 40 pc, masses of 600M_sun_, and ages of 8X10^6^ yr, where the age is estimated from the V magnitudes of the three brightest main-sequence stars. One-third of the Wolf-Rayet stars in this region of the galaxy lie more than 75 pc away from the nearest OB association. Thus, in this galaxy, the most massive stars do not form exclusively in large associations. A comparison of the masses of the associations with the masses of molecular clouds in M33 implies a star formation efficiency of 10%. The OB associations in the southern spiral arm show a weak age gradient perpendicular to the arm, consistent with the presence of a spiral density wave. The associations in the northern arm lack any stars more massive than ~20M_sun_ while the southern arm contains several stars with masses of 60M_sun_. Either a recent cessation of star formation in the inner part of the northern arm or a difference in the upper mass cutoff to the initial mass function between the arms could explain this difference. Publication: The Astronomical Journal Pub Date: May 1991 DOI: 10.1086/115796 Bibcode: 1991AJ....101.1663W Keywords: Astronomical Photometry; B Stars; O Stars; Spiral Galaxies; Charge Coupled Devices; Molecular Clouds; Stellar Evolution; Ubv Spectra; Astrophysics; STARS: EARLY-TYPE; GALAXIES: INDIVIDUAL; GALAXIES: LOCAL GROUP; GALAXIES: STELLAR CONTENT full text sources ADS | data products SIMBAD (1) NED (1)