Range Of Galactocentric Distances Research Articles

THE FLAT OXYGEN ABUNDANCE GRADIENT IN THE EXTENDED DISK OF M83

We have obtained deep multi-object optical spectra of 49 HII regions in the outer disk of the spiral galaxy M83 (=NGC 5236) with the FORS2 spectrograph at the Very Large Telescope. The targets span the range in galactocentric distance between 0.64 and 2.64 times the R25 isophotal radius (5.4-22.3 kpc), and 31 of them are located at R>R25, thus belonging to the extreme outer disk of the galaxy, populated by UV complexes revealed recently by the GALEX satellite. In order to derive the nebular chemical abundances, we apply several diagnostics of the oxygen abundance, including R23, [NII]/[OII] and the [OIII]4363 auroral line, which was detected in four HII regions. We find that, while inwards of the optical edge the O/H ratio follows the radial gradient known from previous investigations, the outer abundance trend flattens out to an approximately constant value. The latter varies, according to the adopted diagnostic, between 12+log(O/H)=8.2 and 12+log(O/H)=8.6 (i.e. from approximately 1/3 the solar oxygen abundance to nearly the solar value). An abrupt discontinuity in the radial oxygen abundance trend is also detected near the optical edge of the disk. These results are tentatively linked to the flat gas surface density in the outskirts of the galaxy, the relatively unevolved state of the extended disk of M83, and the redistribution of chemically enriched gas following a past galaxy encounter.

Galactic rotation curve and the effect of density waves from data on young objects

Based on currently available data on the three-dimensional field of space velocities of young (<50 Myr) open star clusters and the radial velocities of HI clouds and star-forming (HII) regions, we have found the Galactic rotation curve in the range of Galactocentric distances 3 kpc <R<12 kpc using the first six terms of the Taylor expansion of the angular velocity of Galactic rotation in Bottlinger's equations. The Oort constants found are A= 15.5+-0.3 km/s/kpc and B=-12.2+-0.7 km/s/kpc. We have established that the centroid of the sample moves relative to the local standard of rest along the Galactic Y axis with a velocity of -6.2+-0.8 km/s. A Fourier spectral analysis of the velocity residuals from the derived rotation curve attributable to density waves reveals three dominant peaks with wavelengths of 2.5, 1.4, and 0.9 kpc and amplitudes of 4.7, 2.6, and 3.6 km/s, respectively. These have allowed us to estimate the distances between the density wave peaks, 1.9, 2.4, and 3.2 kpc as R increases, in agreement with the description of the density weave as a logarithmic spiral. The amplitude of the density wave perturbations is largest in the inner part of the Galaxy, about 9 km/s, and decreases to approximately 1 km/s in its outer part. A spectral analysis of the radial velocities of young open star clusters has confirmed the presence of periodic perturbations with an amplitude of 5.9+-1.1 km/s and a wavelength 1.7+-0.5 kpc. It shows that the phase of the Sun in the density wave is close to -90 degrees and the Sun is located in the interarm space near the outer edge of the Carina-Sagittarius arm.

The gas kinematics in the Mrk 533 nucleus and circumnuclear region: a gaseous outflow

We present an analysis of 3D spectra of Mrk 533, observed with the integral-field spectrograph MultiPupil Fiber Spectrograph (MPFS) and using the Fabry-Perot Interferometer (FPI) of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) 6-m telescope. We found emissions of gas from the active type 2 Seyfert nucleus in the centre and also from the H ii regions in a spiral structure and a circumnuclear region. The gas kinematics shows regular non-circular motions in the wide range of galactocentric distances from 500 pc up to 15 kpc. The maps of inward and outward radial motions of the ionized gas were constructed. We found that the narrow-line region (NLR) is composed of at least two (probably three) kinematically separated regions. We detect a stratification in the NLR of Mrk 533 with the outflow velocity ranging from 20–50 km s−1 to 600–700 km s−1, respectively, on the radial distances of ∼2.5 and ∼1.5 kpc. The maximal outflow velocity comes from the nucleus and corresponds to the position of the observed radio structure, which is assumed to be created in an approaching jet. We suggest that these ionized gas outflows are triggered by the radio jet intrusion in an ambient medium.

The Galactic halo stellar density distribution from photometric survey data: results of a pilot study

Aims. Our goal is to recover the Galactic halo spatial density by means of field stars. To this aim, we have applied a new technique to the Capodimonte Deep Field (OACDF, Alcala et al. 2004), as a pilot study in view of the VLT Survey Telescope (VST) stellar projects. Considering this unique chance to collect deep and wide-field photometry with the VST, our method may represent a useful tool towards definitive mapping of the Galactic halo. Methods. In the framework of synthetic stellar populations, turn-off stars are used to reconstruct the spatial density. The space density is determined by comparing the data with synthetic color-magnitude diagrams (CMDs). The only assumptions involve the IMF, age, and metallicity of the synthetic halo population. Stars are randomly placed in the solid angle. The contributions of the various Monte Carlo distributions (with a step of 4 kpc) along the line of sight are simultaneously varied to reproduce the observed CMD. Results. Our result for the space density is consistent with a power-law exponent n ≈ 3 over a range of Galactocentric distances from 8 to 40 kpc.

Reconstructing the spatial distribution of the Galactic stellar halo

The VLT Survey Telescope (VST) is going to offer a unique chance to collect deep and wide field photometry in multi-directions, opening the door to a definitive mapping of the Galactic halo. In this shortcoming scenario, we present a pilot study aimed at recovering the halo stellar density using the Capodimonte Deep Field (OACDF, Alcala et al. 2004). Turn-off stars are isolated and the relative color-magnitude diagram (CMD) is compared with synthetic CMDs. Our result is consistent with a power law exponent n ≈ 3 over a range of Galactocentric distances from 8 to 40 kpc.

Abundance gradients in the Milky Way for α elements, iron peak elements, barium, lanthanum, and europium

We model the abundance gradients in the disk of the Milky Way for several chemical elements (O, Mg, Si, S, Ca, Sc, Ti, Co, V, Fe, Ni, Zn, Cu, Mn, Cr, Ba, La and Eu), and compare our results with the most recent and homogeneous observational data. We adopt a chemical evolution model able to well reproduce the main properties of the solar vicinity. The model assumes that the disk formed inside-out with a timescale for the formation of the thin disk of 7 Gyr in the solar vicinity, whereas the halo formed on a timescale of 0.8 Gyr. We adopt new empirical stellar yields derived to best fit the abundances and the abundance ratios in the solar vicinity. We compute, for the first time, the abundance gradients for all the mentioned elements in the galactocentric distance range 4-22 kpc. Comparison with the observed data on Cepheids in the galactocentric distance range 5-17 kpc gives a very good agreement for many of the studied elements. In addition, we well fit the data for the evolution of lanthanum in the solar vicinity, for which we present results here for the first time. We explore, also for the first time, the behavior of the abundance gradients at large galactocentric distances by comparing our results with data relative to distant open clusters and red giants and select the best chemical evolution model on that basis. We find a very good fit to the observed abundance gradients, as traced by Cepheids, for most of the elements, thus confirming the validity of the inside-out scenario for the formation of the Milky Way disk as well as the adopted nucleosynthesis prescriptions. The flat gradients at large galactocentric distances (>12 kpc), as traced by the Cepheids, open cluster and red giant data, lead us to conclude that a model where the density of the halo stellar component is constant in the«inner 20 kpc should be preferred. Other models with different distributions of the halo stellar mass do not produce a good fit of the data.

Wide-Field CCD Photometry around Nine Open Clusters

In this paper we study the evolution of the core and corona of nine open clusters using the projected radial density profiles derived from homogeneous CCD photometric data obtained with the 105 cm Kiso Schmidt telescope. The age and galactocentric distance of the target clusters vary from 16 to 2000 Myr and 9 to 10.8 kpc, respectively. Barring Be 62, which is a young open cluster, other clusters show a uniform reddening across the cluster region. The reddening in Be 62 varies from E(B - V)min = 0.70 mag to E(B - V)max = 1.00 mag. The coronae of six of the clusters in the present sample are found to be elongated; however, on the basis of the present sample it is not possible to establish any correlation between the age and shape of the core. The elongated core in the case of the young cluster Be 62 may reflect the initial conditions in the parental molecular cloud. The other results of the present study are as follows: (1) Core radius rc and corona size rcn/cluster radius rcl are linearly correlated. (2) The rc, rcn, and rcl are linearly correlated with the number of stars in that region. (3) In the age range 10-1000 Myr, the core and corona shrink with age. (4) We find that in the galactocentric distance range 9-10 kpc, the core and corona/cluster extent of the clusters increase with the galactocentric distance.

Probing disk properties with open clusters

We use the open clusters (OCs) with known parameters available in the WEBDA database and in recently published papers to derive properties related to the disk structure. The sample totals 654 OCs, consisting basically of Trumpler types I to III clusters. Because of the completeness effects, the observed radial distribution of OCs with respect to Galactocentric distance does not follow the expected exponential profile. We simulate the effects of completeness assuming that the observed distribution of the number of OCs with a given number of stars above the background, measured in a restricted zone outside the Solar circle, is representative of the intrinsic distribution of OCs throughout the Galaxy. As a result we derive completeness-corrected radial distributions which agree with exponential disks throughout the observed Galactocentric distance range 5--14\,kpc, with scale lengths in the range $1.5 - 1.9\,kpc$. In particular we retrieve the expected exponential-disk radial profile for the highly depleted regions internal to the Solar circle. Extrapolation of the completeness-corrected radial distributions down to the Galactic center indicates a total number of OCs in the range $\rm(1.8 - 3.7)\times10^5$. These estimates are upper-limits because they do not take into account depletion in the number of OCs by dynamical effects in the inner parts of the Galaxy. The observed and completeness-corrected age-distributions of the OCs can be fitted by a combination of two exponential-decay profiles characterized by age scales of $\rm\sim100\,Myr$ and $\rm\sim1.9\,Gyr$, respectively. This rules out evolutionary scenarios based on constant star-formation and OC-disruption rates. We estimate that 3.4--8\% of the embedded clusters do actually emerge from the parent molecular clouds as OCs.

A Library of Integrated Spectra of Galactic Globular Clusters

We present a new library of integrated spectra of 40 Galactic globular clusters, obtained with the Blanco 4 m telescope and the R-C spectrograph at the Cerro Tololo Inter-American Observatory. The spectra cover the range ~3350-6430 Å with ~3.1 Å (FWHM) resolution. The spectroscopic observations and data reduction were designed to integrate the full projected area within the cluster core radii in order to properly sample the light from stars in all relevant evolutionary stages. The S/N values of the flux-calibrated spectra range from 50 to 240 Å-1 at 4000 Å and from 125 to 500 Å-1 at 5000 Å. The selected targets span a wide range of cluster parameters, including metallicity, horizontal-branch morphology, Galactic coordinates, Galactocentric distance, and concentration. The total sample is thus fairly representative of the entire Galactic globular cluster population and should be valuable for comparison with similar integrated spectra of unresolved stellar populations in remote systems. For most of the library clusters, our spectra can be coupled with deep color-magnitude diagrams and reliable metal abundances from the literature to enable the calibration of stellar population synthesis models. In this paper we present a detailed account of the observations and data reduction. The spectral library is publicly available in electronic format from the National Optical Astronomical Observatory Web site.

Carbon and Oxygen Galactic Gradients: Observational Values from H ii Region Recombination Lines

We present results of deep echelle spectrophotometry of eight Galactic H ii regions located at Galactocentric distances between 6.3 and 10.4 kpc. The data have been taken with the Very Large Telescope Ultraviolet Echelle Spectrograph in the 3100–10360 range. We have derived C and O abundances from recombination lines for u A all the objects as well as O abundances from this kind of line for three of the nebulae. The intensity of recombination lines is almost independent of the assumed electron temperature as well as of the possible presence of spatial temperature variations or fluctuations inside the nebulae. These data allow the determination of the gas-phase C and O abundance gradients of the Galactic disk, of paramount importance for chemical evolution models. This is the first time the C gradient is derived from such a large number of H ii regions distributed in such a wide range of Galactocentric distances. Abundance gradients are found of the form dex kpc 1 , D log (O/H) p 0.044 0.010 dex kpc 1 , and dex kpc 1 . D log (C/H) p 0.103 0.018 D log (C/O) p 0.058 0.018 Subject headings: Galaxy: abundances — H ii regions — ISM: abundances

On the oxygen abundance in our Galaxy

The compilation of published spectra of Galactic HII regions with available diagnostic [OIII]4363 line has been carried out. Our list contains 71 individual measurements of 13 HII regions in the range of galactocentric distances from 6.6 to 14.8 kpc. The oxygen abundances in all the HII regions were recomputed in the same way, using the classic Te - method. The oxygen abundance at the solar galactocentric distance traced by those HII regions is in agreement with the oxygen abundance in the interstellar medium in the solar vicinity derived with high precision from the interstellar absorption lines towards stars. The derived radial oxygen abundance distribution was compared with that for HII regions from the Shaver et al. (1983) sample which is the basis of many models for the chemical evolution of our Galaxy. It was found that the original Shaver et al.'s oxygen abundances are overestimated by 0.2-0.3 dex. Oxygen abundances in HII regions from the Shaver et al. sample have been redetermined with the recently suggested P - method. The radial distribution of oxygen abundances from the Shaver et al. sample redetermined with the P - method is in agreement with our radial distribution of (O/H)_Te abundances.

Kinematic parameters of young subsystems and the galactic rotation curve

We analyze the space velocities of blue supergiants, long-period Cepheids, and young open star clusters (OSCs), as well as the H I and H II radial-velocity fields by the maximum-likelihood method. The distance scales of the objects are matched both by comparing the first derivatives of the angular velocity Ω′ determined separately from radial velocities and proper motions and by the statistical-parallax method. The former method yields a short distance scale (for R 0=7.5 kpc, the assumed distances should be increased by 4%), whereas the latter method yields a long distance scale (for R 0=8.5 kpc, the assumed distances should be increased by 16%). We cannot choose between these two methods. Similarly, the distance scale of blue supergiants should be shortened by 9% and lengthened by 3%, respectively. The H II distance scale is matched with the distance scale of Cepheids and OSCs by comparing the derivatives Ω′ determined for H II from radial velocities and for Cepheids and OSCs from space velocities. As a result, the distances to H II regions should be increased by 5% in the short distance scale. We constructed the Galactic rotation curve in the Galactocentric distance range 2–14 kpc from the radial velocities of all objects with allowance for the difference between the residual-velocity distributions. The axial ratio of the Cepheid+OSC velocity ellipsoid is well described by the Lindblad relation, while σu≈σv for gas. The following rotation-curve parameters were obtained: Ω0=(27.5±1.4) km s−1 kpc−1 and A=(17.1±0.5) km s−1 kpc−1 for the short distance scale (R 0=7.5 kpc); and Ω0=(26.6±1.4) km s−1 kpc−1 and A=(15.4±0.5) km s−1 kpc−1 for the long distance scale (R 0=8.5 kpc). We propose a new method for determining the angular velocity Ω0 from stellar radial velocities alone by using the Lindblad relation. Good agreement between the inferred Ω0 and our calculations based on space velocities suggests that the Lindblad relation holds throughout the entire sample volume. Our analysis of the heliocentric velocities for samples of young objects reveals noticeable streaming motions (with a velocity lag of ∼7 km s−1 relative to the LSR), whereas a direct computation of the perturbation amplitudes in terms of the linear density-wave theory yields a small amplitude for the tangential perturbations.

The Excitation and Metallicity of Galactic HiiRegions fromInfrared Space ObservatorySWS Observations of Mid‐Infrared Fine‐Structure Lines

We present mid-infrared Infrared Space Observatory Short-Wavelength Spectrometer (ISO-SWS) observations of the fine-structure emissions lines [Ne II] 12.8 ?m, [Ne III] 15.6 ?m, [Ne III] 36.0 ?m, [Ar II] 6.99 ?m, [Ar III] 8.99 ?m, [S III] 18.7 ?m, [S III] 33.5 ?m, and [S IV] 10.5 ?m and the recombination lines Br? and Br? in a sample of 112 Galactic H II regions and 37 nearby extra-Galactic H II regions in the LMC, SMC, and M33. We selected our sources from archival ISO-SWS data as those showing prominent [Ne II] 12.8 ?m or [Ne III] 15.6 ?m emissions. The Galactic sources have a wide range in galactocentric distance (0 kpc Rgal 18 kpc), which enables us to study excitation and metallicity variations over large Galactic scales. We detect a steep rise in the [Ne III] 15.6 ?m/[Ne II] 12.8 ?m, [Ar III] 8.99 ?m/[Ar II] 6.99 ?m, and [S IV] 10.5 ?m/[S III] 33.5 ?m excitation ratios from the inner Galaxy outward, and a moderate decrease in metallicity, from ~2 Z? in the inner Galaxy to ~1 Z? in the outer disk. The extra-Galactic sources in our sample show low gas density, low metallicity, and high excitation. We find a good correlation between [Ne III] 15.6 ?m/[Ne II] 12.8 ?m and [Ar III] 8.99 ?m/[Ar II] 6.99 ?m excitation ratios in our sample. The observed correlation is well reproduced by theoretical nebular models that incorporate new-generation wind-driven non-LTE model stellar atmospheres for the photoionizing stars. In particular, the non-LTE atmospheres can account for the production of [Ne III] emission in the H II regions. We have computed self-consistent nebular and stellar atmosphere models for a range of metallicities (0.5-2 Z?). We conclude that the increase in nebular excitation with galactocentric radius is due to an increase in stellar effective temperature (as opposed to a hardening of the stellar spectral energy distributions due to the metallicity gradient). We estimate an integrated [Ne III] 15.6 ?m/[Ne II] 12.8 ?m ratio for the Galaxy of 0.8, which puts it well inside the range of values for starburst galaxies. The good fit between observations and our models support the conclusion of Thornley and coworkers that the low [Ne III] 15.6 ?m/[Ne II] 12.8 ?m ratios observed in extra-Galactic sources are due to global aging effects.

ISO spectroscopy of compact HII regions in the Galaxy

Infrared spectra between 2.3 and 196 were taken towards a sample of 45 compact HII regions using the two spectrometers (SWS and LWS) on board ISO. The primary goal is to determine the distribution of element abundances in the Galaxy, although there are also many other uses of this database. The spectra contain a wealth of information on the ionized gas and the associated photodissociation regions through the atomic fine-structure lines and on the dust properties via the dust emission bands and the continuum. Significant variations are found from source to source in both spectral shape and content. The sample of HII regions spans a wide range in galactocentric distance (from 0 to 22 kpc) enabling to investigate the variations of the nebular properties across the Galactic plane. The observations and the data reduction are described in detail in the present paper. The ISO spectral catalogue of compact HII regions contains the combined SWS-LWS spectra for each of the sources, the fluxes of the atomic fine-structure lines and hydrogen recombination lines, and an inventory of the spectra in terms of molecular lines, dust and ice bands.

Formation of Twin Clusters in a Galactic Tidal Field

The formation of globular clusters is still an unsolved problem. Though most scenarios assume a massive molecular cloud as the progenitor, it is unclear how the cloud is transformed into a star cluster. Here a scheme of supernova (SN) induced cluster formation is investigated. In this scenario the expanding SN shell accumulates the mass of the cloud. This is accompanied by fragmentation resulting in star formation in the shell. If this stellar shell expands sufficiently slowly, its self-gravity leads to a recollapsing shell, thus forming one or several stellar clusters.In this paper N-body simulations of collapsing shells moving on circular orbits in a galactic potential are presented. It is shown that typical shells (105 M⊙, 30 pc) evolve to twin clusters in the galactocentric distance range between 3 and 11 kpc. Their masses show a strong radial trend: on orbits inside 5 kpc both clusters have almost equal mass. Outside 5 kpc the more massive twin cluster contains about 55% of the shell's mass, whereas the mass of the smaller decreases linearily to 15% at 11 kpc. Outside 11 kpc the collapsing shells end up in a single cluster. Inside 3 kpc the shells are tidally disrupted and only fragments substantially less massive than the initial shell survive.

Chemical Abundances of OB Stars in Five OB Associations

We present LTE abundances of magnesium, aluminum, sulfur, and iron and non-LTE abundances of carbon, nitrogen, oxygen, and silicon for a sample of 15 slowly rotating B stars belonging to five OB associations: Cyg OB3, Cyg OB7, Lac OB1, Vul OB1, and Cep OB3. These OB associations lie on the Galactic plane and are situated within 3 kpc of the Sun. Of the eight elements sampled, non-LTE abundances for C, N, O, and Si, as well as LTE abundances for Al and Fe, generally show subsolar abundances, with typical underabundances of ~0.2-0.4 dex. The LTE abundances for Mg and S tend to fall closer to solar values in the five associations. Whether the somewhat larger abundances derived for Mg and S, relative to the other six elements studied, are significantly different will require further work, while the modest, but persistent, underabundances (relative to solar) found for the other elements confirm a number of previous studies of young disk OB stars lying relatively near to the Sun. The five associations studied here do not span a significant range of Galactocentric distances; however, their derived abundances agree with what would be expected based upon previous studies that have mapped abundance versus Galactocentric distance and measured abundance gradients in the Milky Way disk.

Great Circle Tidal Streams: Evidence for a Nearly Spherical Massive Dark Halo around the Milky Way

An all high-latitude sky survey for cool carbon giant stars in the Galactic halo has revealed 75 such stars, of which the majority are new detections. Of these, more than half are clustered on a Great Circle on the sky which intersects the center of Sagittarius dwarf galaxy (Sgr) and is parallel to its proper motion vector, while many of the remainder are outlying Magellanic Cloud C-stars. A pole-count analysis of the carbon star distribution clearly indicates that the Great Circle stream we have isolated is statistically significant, being a 5-6 sigma over-density. These two arguments strongly support our conclusion that a large fraction of the Halo carbon stars originated in Sgr. The stream orbits the Galaxy between the present location of Sgr, 16 kpc from the Galactic center, and the most distant stream carbon star, at ~60 kpc. It follows neither a polar nor a Galactic plane orbit, so that a large range in both Galactic R and z distances are probed. That the stream is observed as a Great Circle indicates that the Galaxy does not exert a significant torque upon the stream, so the Galactic potential must be nearly spherical in the regions probed by the stream. We present N-body experiments simulating this disruption process as a function of the distribution of mass in the Galactic halo. A likelihood analysis shows that, in the Galactocentric distance range 16 kpc < R < 60 kpc, the dark halo is most likely almost spherical. We rule out, at high confidence levels, the possibility that the Halo is significantly oblate, with isodensity contours of aspect q_m < 0.7. This result is quite unexpected and contests currently popular galaxy formation models. (Abridged)

Magnetic and optical spiral arms in the galaxy NGC 6946

The spiral pattern in the nearby spiral galaxy NGC 6946 has been studied using the wavelet transformation technique, applied to galaxy images in polarized and total non-thermal radio emission at lambda lambda3.5 and 6.2 cm, in broadband red light, in the lambda 21.1 cm H I line and in the optical H alpha line. Well-defined, continuous spiral arms are visible in polarized radio emission and red light, where we can isolate a multi-armed pattern in the range of galactocentric distances 1.5-12 kpc, consisting of four long arms and one short spiral segment. The 'magnetic arms' (visible in polarized radio emission) are localized almost precisely between the optical arms. Each magnetic arm is similar in length and pitch angle to the preceding optical arm (in the sense of galactic rotation) and can be regarded as its phase-shifted image. Even details like a bifurcation of an optical arm have their phase-shifted counterparts in the magnetic arms. The average relative amplitude of the optical spiral arms (the stellar density excess over the azimuthal average) grows with galactocentric radius up to 0.3-0.7 at r similar or equal to5 kpc, decreases by a factor of two at r=5-6 kpc and remains low at 0.2-0.3 in the outer parts of the galaxy. By contrast, the magnetic arms have a constant average relative amplitude (the excess in the regular magnetic field strength over the azimuthal average) of 0.3-0.6 in a wide radial range r=1.5-12 kpc. We briefly discuss implications of our findings for theories of galactic magnetic fields.

Star Clusters in M33. I. Detection, Morphology, and Photometry

In this paper we present the discovery of 60 star clusters in 20 multiband Hubble Space Telescope (HST) WFPC2 fields in M33. The fields sample a variety of environments, from outer regions to spiral arms and central regions, as well as a range of galactocentric distances. The HST spatial resolution allowed us to penetrate the crowded, spiral arm regions of M33 yielding the first unbiased, representative sample of star clusters for this galaxy. We discuss the separation of clusters from stellar sources, and from other extended sources such as star-forming regions, H II regions, and supernova remnants. For the clusters we present multiband images and discuss morphology, location, and integrated photometry. Measured cluster colors and magnitudes are presented. The cluster density in our sample as a function of galactocentric distance yields an estimate of 690 total clusters in M33.

Star Clusters in M33. II. Global Properties

We discuss the global physical properties of stellar clusters in M33 and compare them with LMC cluster properties. In a companion paper (Paper I) we have compiled the first unbiased, representative sample of star clusters for this galaxy from Hubble Space Telescope WFPC2 multiband images of 20 fields in M33, sampling a variety of environments from outer regions to spiral arms and central regions, as well as a range of Galactocentric distances. In this paper we fit single-mass King models to cluster surface brightness profiles and find that clusters at all ages have well-relaxed density profiles. Core radii are found to be smaller on average than those of Galactic globular clusters and LMC populous clusters at similar magnitudes. Measurements of integrated photometric properties for 60 clusters are also found in Paper I. By comparing the integrated photometric measurements with evolutionary models and theoretical M/LV ratios, we find that clusters formed continuously in M33 from ~4 × 106-1010 yr and have masses between ~4 × 102 and 3 × 105 M⊙. There is a correlation between the ages and masses of our clusters, the oldest objects being the most massive. The global properties of the M33 clusters are compared with cluster systems of other Local Group galaxies. By studying the photometric properties (magnitudes and colors) of M33 clusters and comparing them with those of LMC clusters, a global picture of the star formation history in these two galaxies emerges.