HII Regions In M33 Research Articles

Spectroscopic Study of M33 with the LAMOST Survey. I. Chemical Gradients from Nebulae

Abstract Morphological and chemical structures of M33 are investigated with the LAMOST DR7 survey. Physical parameters; extinction; chemical composition of He, N, O, Ne, S, Cl, and Ar (where available); and radial velocities were determined for 110 nebulae (95 H ii regions and 15 planetary nebulae) in M33. Among them, 8 planetary nebulae and 55 H ii regions in M33 are newly discovered. We obtained the following O abundance gradients: − 0.199 − 0.030 + 0.030 dex R 25 − 1 (based on 95 H ii regions), − 0.124 − 0.036 + 0.036 dex R 25 − 1 (based on 93 H ii regions), and − 0.207 − 0.174 + 0.160 dex R 25 − 1 (based on 21 H ii regions), utilizing abundances from N2 at O3N2 diagnostics and the T e -sensitive method, respectively. The He, N, Ne, S, and Ar gradients resulted in slopes of − 0.179 − 0.146 + 0.145 , − 0.431 − 0.281 + 0.282 , − 0.171 − 0.239 + 0.234 , − 0.417 − 0.182 + 0.174 , and − 0.340 − 0.157 + 0.156 , respectively, utilizing abundances from the T e -sensitive method. Our results confirm the existence of the negative axisymmetric global metallicity distribution that is assumed in the literature. We noticed one new WC star candidate and one transition W-R WN/C candidate. The grand-design pattern of the spiral structure of M33 is presented.

Spatially resolved study of the physical properties of the ionized gas in NGC 595

We present Integral Field Spectroscopy (IFS) of NGC 595, one of the most luminous HII regions in M33. This type of observations allows studying the variation of the principal emission-line ratios across the surface of the nebula. At each position of the field of view, we fit the main emission-line features of the spectrum within the spectral range 3650-6990A, and create maps of the principal emission-line ratios for the total surface of the region. The extinction map derived from the Balmer decrement and the absorbed H-alpha luminosity show good spatial correlation with the 24 micron emission from Spitzer. We also show here the capability of the IFS to study the existence of Wolf-Rayet (WR) stars, identifying the previously catalogued WR stars and detecting a new candidate towards the north of the region. The ionization structure of the region nicely follows the H-alpha shell morphology and is clearly related to the location of the central ionizing stars. The electron density distribution does not show strong variations within the HII region nor any trend with the H-alpha emission distribution. We study the behaviour within the HII region of several classical emission-line ratios proposed as metallicity calibrators: while [NII]/Ha and [NII]/[OIII] show important variations, the R23 index is substantially constant across the surface of the nebula, despite the strong variation of the ionization parameter as a function of the radial distance from the ionizing stars. These results show the reliability in using the R23 index to characterize the metallicity of HII regions even when only a fraction of the total area is covered by the observations.

A NEW DISTANCE TO M33 USING BLUE SUPERGIANTS AND THE FGLR METHOD

The quantitative spectral analysis of medium resolution optical spectra of A and B supergiants obtained with DEIMOS and ESI at the Keck Telescopes is used to determine a distance modulus of 24.93 +/- 0.11 mag for the Triangulum Galaxy M33. The analysis yields stellar effective temperatures, gravities, interstellar reddening, and extinction, the combination of which provides a distance estimate via the Flux-weighted Gravity--Luminosity Relationship (FGLR). This result is based on an FGLR calibration that is continually being polished. An average reddening of <E(B-V)> ~ 0.08 mag is found, with a large variation ranging from 0.01 to 0.16 mag however, demonstrating the importance of accurate individual reddening measurements for stellar distance indicators in galaxies with evident signatures of interstellar absorption. The large distance modulus found is in good agreement with recent work on eclipsing binaries, planetary nebulae, long period variables, RR Lyrae stars, and also with HST observations of Cepheids, if reasonable reddening assumptions are made for the Cepheids. Since distances based on the tip of the red giant branch (TRGB) method found in the literature give conflicting results, we have used HST ACS V- and I-band images of outer regions of M 33 to determine a TRGB distance of 24.84 +/- 0.10 mag, in basic agreement with the FGLR result. We have also determined stellar metallicities and discussed the metallicity gradient in the disk of M33. We find metallicity of $Z_\odot$ at the center and 0.3 $Z_\odot$ in the outskirts at a distance of one isophotal radius. The average logarithmic metallicity gradient is -0.07 +/- 0.01 dex kpc^-1. However, there is a large scatter around this average value, very similar to what has been found for the HII regions in M33.

STAR FORMATION IN LUMINOUS H II REGIONS IN M33

We present a multiwavelength (ultraviolet, infrared, optical and CO) study of a set of luminous HII regions in M33: NGC 604, NGC 595, NGC 592, NGC 588 and IC131. We study the emission distribution in the interiors of the HII regions to investigate the relation between the dust emission at 8 micron and 24 micron and the location of the massive stars and gas. We find that the 24 micron emission is closely related to the location of the ionized gas, while the 8 micron emission is more related to the boundaries of the molecular clouds consistently with its expected association with photodissociation regions (PDRs). Ultraviolet emission is generally surrounded by the H-alpha emission. For NGC 604 and NGC 595, where CO data are available, we see a radial gradient of the emission distribution at the wavelengths studied here: from the center to the boundary of the HII regions we observe ultraviolet, H-alpha, 24 micron, 8 micron and CO emission distributions. We quantify the star formation for our HII regions using the integrated fluxes at the set of available wavelengths, assuming an instantaneous burst of star formation. We show that a linear combination of 24 micron and H-alpha emission better describes the star formation for these objects than the dust luminosities by themselves. For NGC 604, we obtain and compare extinction maps derived from the Balmer decrement and from the 24 micron and H-alpha emission line ratio. Although the maps show locally different values in extinction, we find similar integrated extinctions derived from the two methods. We also investigate here the possible existence of embedded star formation within NGC 604.

The S2N2 metallicity calibrator and the abundance gradient of M 33

We introduce the log(Ha/[SII]6717+6731) vs. log(Ha/[NII]6583) (S2N2) diagnostic diagram as metallicity and ionisation parameter indicator for HII regions in external galaxies. The location of HII regions in the S2N2 diagram was studied both empirically and theoretically. We found that, for a wide range of metallicities, the S2N2 diagram gives single valued results in the metallicity-ionisation parameter plane. We demonstrate that the S2N2 diagram is a powerful tool to estimate metallicities of high-redshift (z ~ 2) HII galaxies. Finally, we derive the metallicity for 76 HII regions in M33 from the S2N2 diagram and calculate an O/H abundance gradient for this galaxy of -0.05 (+-0.01) dex kpc^-1.

Water masers in the Local Group of galaxies

Received; accepted Abstract. We compare the number of detected 22 GHz H2O masers in the Local Group galaxies M31, M33, NGC 6822, IC 10, IC 1613, DDO 187, GR8, NGC 185, and the Magellanic Clouds with the water maser population of the Milky Way. To accomplish this we searched for water maser emission in the two Local Group galaxies M33 and NGC 6822 using the Very Large Array (VLA) and incorporated results from previous studies. We observed 62 Hii regions in M33 and 36 regions with Hemission in NGC 6822. Detection limits are 0.0015 and 0.0008 L⊙ for M33 and NGC 6822, respectively (corresponding to 47 and 50 mJy in three channels with 0.7 km s −1 width). M33 hosts three water masers above our detection limit, while in NGC 6822 no maser source was detected. We find that the water maser detection rates in the Local Group galaxies M31, M33, NGC 6822, IC 1613, DDO 187, GR8, NGC 185, and the Magellan ic Clouds are consistent with expectations from the Galactic water masers if one considers the different star formation rates of the galaxies. However, the gal axy IC 10 exhibits an overabundance of masers, which may result from a compact central starburst.

Kinematical Study of Old HII Regions and Optical Counterpart to the DRAO Canadian Galactic Plane Survey

AbstractThis project aims to tackle a few unresolved problems related to the interstellar medium (ISM) by acting as an optical counterpart to the Canadian Galactic Plane Survey (CGPS). We have three main objectives: (1) the study of large/old HII regions; (2) observations of targets-of-opportunity that may be found by the CGPS; (3) comparison of the kinematics of extragalactic (M33) and galactic HII regions. (1) Old HII regions having large spatial extents will be observed to establish their kinematical structure when almost no molecular material is left to produce photodissociated flows. Does turbulence play a role in these objects as for younger nebulae? (2) Ionised nebulae observed by the CGPS that are peculiar, either morphologically or by special association with neutral hydrogen, will also be observed. (3) The kinematical behaviour of old HII regions in M33 will be compared with that of galactic HII regions. With both data sets in hand we will check if HII regions, like supernovae, dump energy into the neutral ISM. The instrument used as well as some very preliminary data are presented.

A criterion for identification of OB associations and star complexes

Abstract A new objective automated method for identification of OB associations and star complexes is proposed. It is suitable for a reliable comparison of the stellar groups in nearby galaxies. The method was applied for the galaxy M33. The criterion identifies three hierarchic groups in M33: OB association, aggregates, and star complexes. The select stellar groups show strong correlations with the HII regions in M33. The average size of the stellar associations, aggregates, and star complexes are 80 pc, 190 and 600 pc, respectively.

Radio Observations of Hii Regions in M33

The Westerbork Synthesis Radio Telescope was used to map the continuum radiation of M33 at 1415 MHz. Of 67 radio sources with fluxes S&gt; 1.8 mJy (3σ), 60% coincide with Hα sources. These are all intrinsically stronger than 4 × the Orion nebula, i.e., they are giant Hiiregions. The two strongest sources, NGC 604 (58 mJy) and NGC 595 (20 mJy), are similar to W51.