Starburst Galaxy M82 Research Articles

GALEX Observations of the Ultraviolet Halos of NGC 253 and M82

We present Galaxy Evolution Explorer (GALEX) images of the prototypical edge-on starburst galaxies M82 and NGC 253. Our initial analysis is restricted to the complex of ultraviolet (UV) filaments in the starburst-driven outflows in the galaxy halos. The UV luminosities in the halo are too high to be provided by continuum and line emission from shock-heated or photoionized gas, except perhaps in the brightest filaments in M82, suggesting that most of the UV light is the stellar continuum of the starburst scattered into our line of sight by dust in the outflow. This interpretation agrees with previous results from optical imaging polarimetry in M82. The observed luminosity of the halo UV light is lesssim0.1% of the bolometric luminosity of the starburst. The morphology of the UV filaments in both galaxies shows a high degree of spatial correlation with and X-ray emission. This indicates that these outflows contain cold gas and dust, some of which may be vented into the intergalactic medium (IGM). UV light is seen in the Hα 11 kpc north of M82. If this cap is a result of the wind fluid running into a preexisting gas cloud, the gas cloud contains dust and is not primordial in nature, but was probably stripped from M82 or M81. If starburst winds efficiently expel dust into the IGM, this could have significant consequences for the observation of cosmologically distant objects.

Deep Radio Imaging with MERLIN of the Supernova Remnants in M82

SummaryAn 8 day MERLIN deep integration at 5GHz of the central region of the starburst galaxy M82 has been used to investigate the radio structure of a number of supernova remnants in unprecedented detail revealing new shells and partial shell structures for the first time. In addition, by comparing the new deep 2002 image with an astrometrically aligned image from 36 hours of data taken in 1992, it has been possible to directly measure the expansion velocities of 4 of the most compact remnants in M82. For the two most compact remnants, 41.95+575 and 43.31+592, expansion velocities of 2800 ± 300 km s-1 and 8750 ± 400kms-1have been derived. These confirm and refine the measured expansion velocities which have been derived from VLBI multi-epoch studies. For remnants 43.18+583 and 44.01+596, expansion velocities of 10500 ± 750km s-1 and 2400 ± 250 kms-1have been measured for the first time. In addition, the peak of the radio emission for SNR 45.17+612 has moved between the two epochs implying velocities around 7500km s-1. The relatively compact remnants in M82 are thus found to be expanding over a wide range of velocities which appear unrelated to their size. The new 2002 map is the most sensitive high-resolution image yet made of M82, achieving an rms noise level of 17μJy beam-1. This establishes a first epoch for subsequent deep studies of expansion velocities for many SNR within M82.

SUBARU/FOCAS Globular Clusters Survey around M82

Recently, a number of possible young globular clusters (GCs) have been found in some merging/interacting galaxies or starburst galaxies. On the other hand, it is well known that GCs are numerous in giant elliptical galaxies many of which are thought to be formed via major merger of galaxies. These facts lead us to a thought that the formation process of GCs could accompany galaxy – galaxy interaction followed by starburst. The archetypical starburst galaxy M82 is an ideal target to study the relation between galaxy interaction, starburst, and GC formation.

Very Large Array H92α and H53α Radio Recombination Line Observations of M82

We present high angular resolution (06) observations made with the Very Large Array of the radio continuum at 8.3 and 43 GHz, as well as H92α and H53α radio recombination lines from the nearby (~3 Mpc) starburst galaxy M82. In the continuum we identify 58 sources at 8.3 GHz, of which 19 have no counterparts in catalogs published at other frequencies. At 43 GHz we identify 18 sources, unresolved at 06 resolution, of which five were unknown previously. The spatial distribution of the H92α line is inhomogeneous; we identify 27 features; about half of them are associated with continuum emission sources. Their sizes are typically in the range 2-10 pc. Although observed with poorer signal-to-noise ratio, the H53α line is detected. The line and continuum emission are modeled using a collection of H II regions at different distances from the nucleus. The observations can be interpreted assuming a single-density component, but equally well with two components if constraints originating from previous high-resolution continuum observations are used. The high-density component has a density of ~4 × 104 cm-3. However, the bulk of the ionization is in regions with densities that are typically a factor of 10 lower. The gas kinematics, using the H92α line, confirms the presence of steep velocity gradient (26 km s-1 arcsec-1) in the nuclear region, as previously reported, in particular from observations of the [Ne II] line at 12 μm. This gradient has about the same amplitude on both sides of the nucleus. Since this steep gradient is observed not only on the major axis but also at large distances along a band at P.A. ~ 150°, the interpretation in terms of x2 orbits elongated along the minor axis of the bar, which would be observed at an angle close to the inclination of the main disk, seems inadequate. The observed kinematics cannot be modeled using a simple model that consists of a set of circular orbits observed at different tilt angles. Ad hoc radial motions must be introduced to reproduce the pattern of the velocity field. Different families of orbits are indicated since we detect a signature in the kinematics at the transition between the two plateaus observed in the NIR light distribution. These H92α data also reveal the base of the outflow where the injection toward the halo on the northern side occurs. The outflow has a major effect on the observed kinematics, present even in the disk at distances close to the nucleus. The kinematic pattern suggests a connection between the gas flowing in the plane of M82 toward the center; this behavior most likely is due to the presence of a bar and the outflow out of the plane.

Intermediate mass black holes in accreting binaries: formation, evolution and observational appearance

We study the origin of the ultraluminous X-ray source M82 X-1 in the nearby starburst galaxy M82. This X-ray source is of particular interest as it is currently the best candidate for an intermediate mass black hole; it is associated with a 54mHz quasi-periodic oscillation with a relatively low (~1 keV) blackbody temperature. We perform detailed binary evolution calculations of 2-15 Msolar stars which transfer mass to a 100-2000 Msolar black hole and present an empirical model for the X-ray characteristics expected for such binaries. Based on the binary evolution calculations and the assumption in our simulations we conclude that the most likely candidate for the bright X-ray source M82 X-1 is a 10-15 Msolar star near the end of its main sequence or slightly evolved, which transfers mass to a ~1000 Msolar black hole. We expect the system to be in the high/soft state. In that case the binary will not be visible as a source of gravitational wave radiation, but other transient X-ray binaries with lower mass donors way be rather bright sources of gravitational wave radiation.

Near‐Infrared Molecular Hydrogen Emission from the Central Regions of Galaxies: Regulated Physical Conditions in the Interstellar Medium

The central regions of many interacting and early-type spiral galaxies are actively forming stars. This process affects the physical and chemical properties of the local interstellar medium, as well as the evolution of the galaxies. We observed near-infrared H2 emission lines: v ¼ 1 0 S(1), 3–2 S(3), 1–0 S(0), and 2–1 S(1) from the central � 1 kpc regions of the archetypical starburst galaxies M82 and NGC 253 and the less dramatic but still vigorously star-forming galaxies NGC 6946 and IC 342. Like the far-infrared continuum luminosity, the nearinfrared H2 emission luminosity can directly trace the amount of star formation activity because the H2 emission lines arise from the interaction between hot and young stars and nearby neutral clouds. The observed H2 line ratios show that both thermal excitation and nonthermal excitation are responsible for the emission lines but that the great majority of the near-infrared H2 line emission in these galaxies arises from energy states excited by ultraviolet fluorescence. The derived physical conditions, e.g., far-ultraviolet radiation field and gas density, from [C ii ]a nd [O i] lines and far-infrared continuum observations when used as inputs to photodissociation models also explain the luminosity of the observed H2 1–0S(1) line. The ratio of the H2 1–0S(1) line to far-IR continuum luminosity is remarkably constant over a broad range of galaxy luminosities: LH2 =LFIR ’ 10 � 5 , in normal late-type galaxies (including the Galactic center), in nearby starburst galaxies, and in luminous IR galaxies (LIRGs: LFIR >10 11 L� ). Examining this constant ratio in the context of photodissociation region models, we conclude that it implies that the strength of the incident UV field on typical molecular clouds follows the gas density at the cloud surface. Subject headings: galaxies: individual(M82,NGC 253,NGC6946,IC 342) — galaxies: ISM — galaxies:spiral — galaxies: starburst — infrared: ISM — ISM: lines and bands

Ultraluminous X-Ray Sources as Intermediate-Mass Black Holes Fed by Tidally Captured Stars

The nature of ultraluminous X-ray (ULX) sources is presently unknown. A possible explanation is that they are accreting intermediate-mass black holes (IBHs) that are fed by Roche lobe overflow from a tidally captured stellar companion. We show that a star can circularize around an IBH without being destroyed by tidal heating (in contrast to the case of massive black holes in galactic centers, where survival is unlikely). 6 M 1 10 M BH , We find that the capture and circularization rate is ∼ yr 1 , almost independently of the cluster’s relaxation 8 5 # 10 time. We follow the luminosity evolution of the binary system during the main-sequence Roche lobe overflow phase and show it can maintain ULX source–like luminosities for greater than 10 7 yr. In particular, we show that the ULX source in the young cluster MGG-11 in starburst galaxy M82, which possibly harbors an IBH, is well explained by this mechanism, and we predict that 10% of similar clusters with IBHs have a tidally captured circularized star. The cluster can evaporate on a timescale shorter than the lifetime of the binary. This raises the possibility of a ULX source that outlives its host cluster, or even lights up only after the cluster has evaporated, in agreement with observations of hostless ULX sources. Subject headings: black hole physics — galaxies: star clusters — stellar dynamics — X-rays: binaries

Globular Cluster Formation in M82

We present high-resolution mid-infrared (mid-IR; 11.7 and 17.65 ?m) maps of the central 400 pc region of the starburst galaxy M82. Seven star-forming clusters are identified, which together provide ~15% of the total mid-IR luminosity of the galaxy. We find that these young stellar clusters have inferred masses and sizes comparable to globular clusters. At least 20% of the star formation in M82 is found to occur in super star clusters.

Stellar and Gaseous Abundances in M82

The near infrared (IR) absorption spectra of starburst galaxies show several atomic and molecular lines from red supergiants which can be used to infer reliable stellar abundances. The metals locked in stars give a picture of the galaxy metallicity prior to the last burst of star formation. The enrichment of the new generation of stars born in the last burst can be traced by measuring the hot gas in the X-rays. For the first time detailed stellar abundances in the nuclear region of the starburst galaxy M82 have been obtained. They are compared with those of the hot gas as derived from an accurate re-analysis of the XMM and Chandra nuclear X-ray spectra. The cool stars and the hot gas suggest [Fe/H]=-0.35+/-0.2 dex, and an overall [Si,Mg/Fe] enhancement by 0.4 and 0.5 dex, respectively. This is consistent with a major chemical enrichment by SNe II explosions in recursive bursts on short timescales. Oxygen is more puzzling to interpret since it is enhanced by 0.3 dex in stars and depleted by 0.2 dex in the hot gas. None of the standard enrichment scenarios can fully explain such a behavior when compared with the other alpha-elements.

The Effect of Tidal and Stellar Mass Loss on Compact Stars Clusters in the Galaxy M82

Compact star clusters in star burst galaxies sink towards galactic centers due to dynamical friction. If they survive against mass loss from stellar evolution and tidal stripping from their parent galaxy, they can bring intermediate-mass black holes (of about 1000M), which are produced in the clusters by runaway merging of massive stars, into the centers which can then merge and form a supermassive black hole (Ebisuzaki et al., Astrophys. J. 562 (2001), L19). We investigate survival conditions for the clusters using numerical simulations which include stellar evolution and tidal stripping. Our gravitational N-body simulations use MDGRAPE-2 (http://www.peta.co.jp/), modeling star clusters in the star burst galaxy M82. We find that the condition for survival strongly depends on the initial mass function of the cluster. If a star cluster has a power law IMF with α ≤ -2.5, it can sink down to the center of the parent galaxy. These results support the formation scenario of supermassive black holes described above.

M82 X-1

By using ASCA and Chandra, we discovered a bright X-ray source M82 X-1 in the starburst galaxy M82. The peak luminosity of ∼1× 1041 ergs sec-1 and the location of off-center position of M82 in the starburst galaxy M82 suggest that M82 X-1 is a new type of black hole, intermediate massive black hole (IMBH). We also found an expanding molecular super bubble (EMSB) surrounding the IMBH. We propose a hypothesis that the IMBH was formed in the starburst activity 106∼107 yrs ago. We review the course of the discovery and show recent progress on studies of the X-ray spectrum and the position of M82 X-1.

The M82 Outflow: X-rays as a Probe for Neutral Disk Gas

We present an analysis of X-ray absorption in the nearby starburst galaxy M82. The X-ray attenuating column densities in the northern part of the M 82 outflow can be associated with cold disk gas detected in maps of H1 and CO (1→0). We derive an XCO factor which is somewhat lower as compared to that in our Galaxy. This is in good agreement with multi-transition line studies of various molecules in the disk of M 82.

Deep Near‐Infrared Imaging of a Field in the Outer Disk of M82 with the Altair Adaptive Optics System on Gemini‐North

ABSTRACTDeep H and K′ images recorded with the Altair adaptive optics system and Near‐Infrared Imager on Gemini‐North are used to probe the red stellar content in a field with a projected distance of 1 kpc above the disk plane of the starburst galaxy M82. The data have an angular resolution of 008 FWHM, and individual asymptotic giant branch (AGB) and red giant branch (RGB) stars are resolved. The AGB extends to at least 1.7 mag in K above the RGB tip, which occurs at K = 21.7. The relative numbers of bright AGB stars and RGB stars are consistent with stellar evolution models, and one of the brightest AGB stars has an H−K color and K brightness that is consistent with it being a C star. The brightnesses of the AGB stars suggest that they formed during intermediate epochs, possibly after the last major interaction with M81. Therefore, star formation in M82 during intermediate epochs may not have been restricted to the plane of the disk.

ChandraObservations of Expanding Shells in the Dwarf Starburst Galaxy NGC 3077

Deep Chandra observations (53 ks, ACIS-S3) of NGC 3077, a starburst dwarf galaxy in the M81 triplet, resolve the X-ray emission from several supershells. The emission is brightest in the cavities defined by expanding shells detected previously in Hα emission. Thermal emission models fitted to the data imply temperatures ranging from ~1.3 to 4.9 × 106 K and indicate that the strongest absorption is coincident with the densest clouds traced by CO emission. The fitted emission measures give pressures of P/k ≈ (105-106)ξ-0.5f K cm-3 (where ξ is the metallicity of the hot gas in solar units and fv is the volume filling factor). Despite these high pressures, the radial density profile of the hot gas is not as steep as that expected in a freely expanding wind (e.g., as seen in the neighboring starburst galaxy M82), implying that the hot gas is still confined by the Hα shells. The chaotic dynamical state of NGC 3077 undermines reliable estimates of the escape velocity. The more relevant quantity for the ultimate fate of the outflow is probably the gas density in the rich intragroup medium. Based on the H I distribution of NGC 3077 and a connected tidal tail we argue that the wind has the potential to leave the gravitational well of NGC 3077 to the north but not to the south. The total 0.3-6.0 keV X-ray luminosity is ~(2-5) × 1039 ergs s-1 (depending on the selected thermal plasma model). Most (~85%) of the X-ray luminosity in NGC 3077 comes from the hot interstellar gas; the remainder comes from six X-ray point sources. In spite of previous claims to the contrary, we do not find X-ray emission originating from the prominent tidal tail near NGC 3077.

First-look XMM-Newton EPIC observations of the prototypical starburst galaxy M82

We present initial XMM‐Newton EPIC observations of the prototypical starburst galaxy M82. The superwind is seen to extend continuously from the starburst region to the X-ray emission associated with the Hα ‘cap’. We also find evidence for a ridge feature, probably associated with the superwind interacting with an H I streamer. Narrow-band images, centred on individual X-ray lines, show differences in morphology, with higher energy lines being less spatially extended, and a systematic shift with energy in the region of peak emission. Spectral fits with two thermal and one power-law component provide a good fit to the spectra of the nuclear and inner wind regions, indicating a multiphase superwind. We discuss the implications of these observations on our understanding of superwinds.

Anisotropy at the end of the cosmic ray spectrum?

The starburst galaxies M82 and NGC253 have been proposed as the primary sources of cosmic rays with energies above ${10}^{18.7}\mathrm{eV}.$ For energies $\ensuremath{\gtrsim}{10}^{20.3}\mathrm{eV}$ the model predicts strong anisotropies. We calculate the probabilities that the latter can be due to chance occurrence. For the highest energy cosmic ray events in this energy region, we find that the observed directionality has less than 1% probability of occurring due to random fluctuations. Moreover, during the first 5 years of operation at Auger, the observation of even half the predicted anisotropy has a probability of less than ${10}^{\ensuremath{-}5}$ to occur by chance fluctuation. Thus, this model can be subject to test at very small cost to the Auger priors budget and, whatever the outcome of that test, valuable information on the galactic magnetic field will be obtained.

A12COJ = 6–5 Map of M82: The Significance of Warm Molecular Gas

We present a 12 CO J ¼ 6–5 map of the nuclear regions of the starburst galaxy M82 at a resolution of 14 00 taken at the Caltech Submillimeter Observatory (CSO). Hot spots were found on either side of the dynamical center. We compare our results with a high-resolution 12 CO J ¼ 2–1 interferometer map, and present a 12 CO J ¼ 6–5/ 12 CO J ¼ 2–1 line ratio map obtained using a novel deconvolution technique. This line ratio is highest at the two J ¼ 6–5 integrated intensity peaks, reaching 0.4 and 0.5 in the northeast and southwest peaks, respectively, and is typically 0.2 elsewhere in the nuclear region. We also present measurements of 12 CO J ¼ 4–3, 12 CO J ¼ 3–2, and 13 CO J ¼ 3–2, and an upper limit for 13 CO J ¼ 6–5. We analyze these observations in the context of a two-component large velocity gradient (LVG) excitation model. Likelihood density curves were calculated for each of the model parameters and a variety of related physical quantities for the northeast and southwest peaks based on the measured line intensities and their associated uncertainties. This approach reveals in an unbiased way how well various quantities can be constrained by the CO observations. We find that the beam-averaged 12 CO and 13 CO column densities, the isotopomer abundance ratio, and the area filling factors are among the best constrained quantities, while the cool component H2 density and pressure are less well constrained. The results of this analysis suggest that the warm gas is less dense than the cool gas, and that over half of the total molecular gas mass in these nuclear regions is warmer than 50 K. Subject headings: galaxies: individual (M82) — galaxies: ISM — galaxies: starburst — submillimeter

Discovery of X-Ray Quasi-periodic Oscillations from an Ultraluminous X-Ray Source in M82: Evidence against Beaming

We report the discovery with the European Photon Imaging Camera CCDs on board XMM-Newton of a 54 mHz quasi-periodic oscillation (QPO) in the greater than 2 keV X-ray flux from an ultraluminous X-ray source (ULX) in the starburst galaxy M82. This is the first detection of a QPO in the X-ray flux from an extragalactic ULX and confirms that the source is a compact object. On the basis of the QPO strength and previous Chandra observations, it appears likely that the QPO is associated with the most luminous object in the central region of M82, CXO M82 J095550.2+694047; however, XMM imaging alone is not sufficient to unambiguously confirm this. The other plausible candidate is CXO M82 J095551.1+694045; however, the QPO luminosity is comparable to the peak luminosity of this object in Chandra observations, which argues against it being the source of the QPO. The QPO had a centroid frequency of 54.3 ± 0.9 mHz, a coherence Q ≡ ν0/Δνfwhm ≈ 5, and an amplitude (rms) in the 2-10 keV band of 8.5%. Below 0.2 Hz, the power spectrum can be fitted by a power law with index ≈1 and amplitude (rms) of 13.5%. The X-ray spectrum requires a curving continuum, with a disk blackbody at T = 3.1 keV providing an acceptable fit. A broad Fe line centered at 6.55 keV is required in all fits, but the equivalent width is sensitive to the continuum model. There is no evidence of a reflection component. The implied bolometric luminosity is ≈ × 1040 ergs s-1. Archival Rossi X-Ray Timing Explorer pointings at M82 also show evidence for QPOs in the 50-100 mHz frequency range. We discuss the implications of our findings for models of ULXs.

The [F[CLC]e[/CLC] [CSC]ii[/CSC]] 1.644 Micron Emission in M82 and NGC 253: Is It a Measure of the Supernova Rate?

We present Hubble Space Telescope NICMOS [Fe II] 1.644 μm, Paα (1.87 μm), and continuum images of the starburst galaxies M82 and NGC 253 at an unprecedented spatial resolution. In both galaxies we detect [Fe II] compact sources superposed on a diffuse background in the disk of the galaxies, together with a component above and below the plane of the galaxy. The radio and [Fe II] emissions perpendicular to the disk of M82 show a remarkable similarity to each other, suggesting that both emissions originate in shocks from supernova explosions. We find a spatial correspondence between bright compact [Fe II]–emitting regions and the location of radio supernova remnants (SNRs) for approximately 30%–50% of radio SNRs in M82 and NGC 253. This lack of a one-to-one correspondence, more than being indicative of a different origin for the radio and [Fe II] emission in starbursts, suggests two populations of SNRs: an older population (104 yr), traced by the [Fe II] emission, and a younger population (a few hundred years old), traced by the radio SNRs. We therefore conclude that the [Fe II] emission in starburst galaxies provides a good estimate of the supernova activity. Using our newly determined [Fe II] luminosities (corrected for extinction) of M82 and NGC 253, we reevaluate the calibration of the supernova rate in terms of the [Fe II] luminosity for starburst galaxies.

Missing Link Found? — The “runaway” path to supermassive black holes

Observations of stellar kinematics, gas dynamics and masers around galactic nuclei have now firmly established that many galaxies host central supermassive black holes (SMBHs) with masses in the range 106 ∼ 109M⊙. However, how these SMBHs formed is not well understood. One reason for this situation is the lack of observations of intermediate-mass BHs (IMBHs), which could bridge the gap between stellar-mass BHs and SMBHs. Recently, this missing link (i.e., an IMBH) has been found in observations made by ASCA and Chandra of the central region of the starburst galaxy M82 (Matsumoto and Tsuru 1999, Ptak and Griffith 1999, Matsumoto et al. 2001, Kaaret et al. 2001). Subsequent observations by SUBARU have revealed that this IMBH apparently coincides with a young compact star cluster. Based on these findings, we propose a new formation scenario for SMBHs. In this scenario, IMBHs first form in young compact star clusters through runaway merging of massive stars. While these IMBHs are forming, the host star clusters sink toward the galactic nucleus through dynamical friction, and upon evaporation deposit their IMBHs near the galactic center. The IMBHs then form binaries and eventually merge via gravitational radiation, forming an SMBH.