arXiv subjects

Elias Brinks

Publications and source records attributed to Elias Brinks.

94 records · Page 6Linked to original sources

arXiv1999

Holes and Shells in the Interstellar Medium of the Nearby Dwarf Galaxy IC 2574

We present HI synthesis observations of the nearby dwarf galaxy IC 2574 (a member of the M81 group of galaxies) made with the NRAO Very Large Array at high spatial and velocity resolution (95 pc x 2.6 km/s). The VLA HI observations show a stunning amount of detail in the form of 48 mostly expanding HI shells and holes in its neutral interstellar medium. These features range in size from about 100 (a limit set by the size of the beam) to about 1000 pc dominating the appearance of the HI surface brightness map. Their dynamics clearly influence the velocity field of IC 2574. Current star formation, as traced by H-alpha emission, is predominantly found along the rims of the larger HI holes, suggesting propagating star formation. On linear scales of about 95 pc, star formation occurs if the HI surface density reaches values higher than 10^21 cm^-2. The scaleheight of the HI layer is found to be about 350 pc, considerably thicker than that in massive disk galaxies. This is due to a lower gravitational potential (for the same observed onedimensional velocity dispersion of about 7 km/s). A comparison with other galaxies shows that the energies needed to create the expanding HI structures are the same for all types of galaxies, at least to first order. The overall statistical properties of the HI holes and shells in galaxies show clear trends with Hubble type (or rather mass), such as in their diameter distribution, expansion velocities and ages.

astro-ph↗

arXiv1998

Ring structure and warp of NGC5907 -- Interaction with dwarf galaxies

The edge-on, nearby spiral galaxy NGC5907 has long been used as the prototype of a ``non-interacting'' warped galaxy. We report here the discovery of two interactions with companion dwarf galaxies that substantially change this picture. First, a faint ring structure is discovered around this galaxy that is likely due to the tidal disruption of a companion dwarf spheroidal galaxy. The ring is elliptical in shape with the center of NGC5907 close to one of the ring's foci. This suggests the ring material is in orbit around NGC5907. No gaseous component to the ring has been detected either with deep H$α$ images or in Very Large Array (VLA) HI 21-cm line maps. The visible material in the ring has an integrated luminosity <= 10^8 L_sun and its brightest part has a color R-I ~ 0.9. All of these properties are consistent with the ring being a tidally-disrupted dwarf spheroidal galaxy. Second, we find that NGC5907 has a dwarf companion galaxy, PGC54419, projected to be only 36.9 kpc from the center of NGC5907, close in radial velocity (ΔV = 45 km s^{-1}) to the giant spiral galaxy. This dwarf is seen at the tip of the HI warp and in the direction of the warp. Hence, NGC5907 can no longer be considered ``non-interacting,'' but is obviously interacting with its dwarf companions much as the Milky Way interacts with its dwarf galaxies. These results, coupled with the finding by others that dwarf galaxies tend to be found around giant galaxies, suggest that tidal interaction with companions, even if containing a mere 1% of the mass of the parent galaxy, might be sufficient to excite the warps found in the disks of many large spiral galaxies.

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arXiv1998

X-ray Emission from an Expanding Supergiant Shell in IC 2574

We present a multi--wavelength study of a supergiant shell within the violent interstellar medium of the nearby dwarf galaxy IC 2574, a member of the M81 group of galaxies. Neutral hydrogen (HI) observations obtained with the Very Large Array (VLA) reveal a prominent expanding supergiant HI shell which is thought to be produced by the combined effects of stellar winds and supernova explosions. It measures roughly 1000 x 500 pc in size and is expanding at about 25 km/s. The HI data suggest an age of about 1.4 x 10^6 yrs; the energy input must have been of order (2.6\pm 1) x 10^53 ergs. Massive star forming regions, as traced by H$α$ emission, are situated predominantly on the rim of this HI shell. VLA radio continuum observations at 6 cm show that these star-forming regions are the main sources of radio continuum emission in this galaxy. Soft X-ray emission from within the HI hole is detected by a pointed ROSAT PSPC observation. The emission is resolved, coinciding in size and orientation with the HI shell. These spatial properties suggest that the emission is generated by an X-ray emitting plasma located within the HI shell although a contribution from X-ray binaries cannot be completely ruled out. The X-ray data are compatible with emission coming from a Raymond & Smith plasma at a temperature of about log(T[K]) = 6.8 and a density of 0.03 cm^-3.

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arXiv1996

The absence of diffuse gas around the dwarf spheroidal galaxy Leo I

We have obtained spectra of three QSO/AGNs with the GHRS aboard the Hubble Space Telescope to search for absorption from low column density gas in the halo of the dwarf spheroidal (dSph) galaxy Leo I. The probe sightlines pass 2.1, 3.7, and 8.1 kpc from the center of the galaxy, but no CIV, SiII, or SiIV absorption is found at the velocity of Leo I. The absence of low ionization species suggests that the column density of neutral hydrogen which exists within 2-4 kpc of the galaxy is N(HI) < 10^{17} cm^{-2}; assuming that the high ionization lines of SiIV and CIV dominate the ionization fraction of silicon and carbon, the limit to the total hydrogen column is N(H) < 10^{18} cm^{-2}. Our results demonstrate that there are no dense flows of gas in or out of Leo I, and that there is no evidence for tidally disrupted gas which might have accompanied the galaxy's formation or evolution. However, our detection limits are insufficient to rule out the existence of a sphere or shell of ionized gas around the dSph, with a mass up to that constituting the entire galaxy. Our models show that dSph galaxies similar to Leo I are not massive enough to have halos which can contribute significantly to the metal line absorption cross-section of QSO absorbers seen at high redshift.

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