We present first results from a Keck/DEIMOS spectroscopic survey of red giant branch (RGB) stars in M33. The radial velocity distributions of the stars in our fields are well described by three Gaussian components, corresponding to a candidate halo component with an uncorrected radial velocity dispersion of σ ≃ 50 km s, a candidate disk component with a dispersion σ ≃ 16 km s, and a third compo...

We observed the nucleus of M33, the third-brightest galaxy in the Local Group, with the Space Telescope Imaging Spectrograph at a resolution at least a factor of 10 higher than previously obtained. Rather than the steep rise expected within the radius of gravitational influence of a supermassive black hole, the random stellar velocities showed a decrease within a parsec of the center of the gal...

Aims. We use different tracers, such as Hα, ultraviolet (UV), and infrared (IR) emissions at various wavelengths, to study the dust and star-formation (SF) conditions throughout the disk of M 33. Methods. We derive the radial distribution of dust, of the old and young stellar population using Spitzer and GALEX data, complemented by ground-based optical data and available surveys of atomic and m...

The nearby galaxy M33 hosts the most luminous steady X-ray source in the Local Group. The high spatial resolution of Chandra allows us to confirm that this ultra-luminous X-ray source is within the nucleus and rule out at the 4.6σ level a previously proposed possible counterpart located 1 away. The X-ray spectrum is well fitted by a disc blackbody with kTin=1.18±0.02 keV and Rin(cos θ)=57±3 km,...

A method for identification of stellar complexes in M 33 is applied. Several OB associations form a stellar complex with mean size of 0.3-1 kpc. We apply a correlation technique to compare different stellar populations in M 33. Our results confirm the existence of a strong correlation between OB stars, H II regions and WR stars, which trace the regions of massive star formation. There is a good...

Fuse spectra of the four brightest H ii regions in M 33 show absorption by interstellar gas in the Galaxy and in M 33. On three lines of sight molecular hydrogen in M 33 is detected. This is the first measurement of diffuse H2 in absorption in a Local Group galaxy other than the Magellanic Clouds. A quantitative analysis is difficult because of the low signal to noise ratio and the systematic e...

Using the theoretical stellar population synthesis models of BC96, Kong et al. (2003) showed that some BATC colors and color indices could be used to disentangle the age and metallicity effect. They found that there is a very good relation between the flux ratio of L8510/L9170 and the metallicity for stellar populations older than 1 Gyr. In this paper, based on the Kong et al. results and on th...

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 0.8–8.0 keV spectrum of X-4 is described by a two-component model, consisting of a thin thermal plasma emission with a temperature of ∼ 1.0keV, and a power law emission with a photon index of ∼ 2.0. T...

We have started a survey of M 33 in order to find variable stars and Cepheids in particular. We have obtained more than 30 epochs of g′r′i′ data with the CFHT and the one-square-degree camera MegaCam. We present first results from this survey, including the search for variable objects and a basic characterization of the various groups of variable stars.