M. López-Corredoira

Old stellar Galactic disc in near-plane regions according to 2MASS: Scales, cut-off, flare and warp

We have pursued two dierent methods to analyze the old stellar population near the Galactic plane, using data from the 2MASS survey. The first method is based on the isolation of the red clump giant population in the color-magnitude diagrams and the inversion of its star counts to obtain directly the density distribution along the line of sight. The second method fits the parameters of a disc model to the star counts in 820 regions. Results from both independent methods are consistent with each other. The qualitative conclusions are that the disc is well fitted by an exponential distribution in both the galactocentric distance and height. There is not an abrupt cut-o in the stellar disc (at least within R 6 kpc) that: the scale- height in the solar circle is hz(R)= 3:6 10 2 R, the scale-length of the surface density is hR= 0:42 R and the scale-length of the space density in the plane (i.e. including the eect of the flare) is H= 0:25 R. The variation of the scale-height due to the flare follows roughly a law hz(R) hz(R )e xp R R (12 0:6R(kpc)) kpc (for R< 15 kpc; R= 7:9 kpc). The warp moves the mean position of the disc to a height zw= 1:2 10 3 R(kpc) 5:25 sin(+ 5) pc (for R< 13 kpc; R= 7:9 kpc).

Tracing the long bar with red-clump giants

Context. Over the last decade a series of results have lent support to t he hypothesis of the existence of a long thin bar in the Milky Way with a half-length of 4.5 kpc and a position angle of around 45 ◦ . This is apparently a very different structure from the triaxial bulge of the Galaxy. Aims. In this paper, we analyse the stellar distribution in the inn er 4 kpc of the Galaxy to see if there is clear evidence for two triaxial or barlike structures, or whether there is only one. Methods. By using the red-clump population as a tracer of the structure of the inner Galaxy we determine the apparent morphology of the inner Galaxy. Star counts from 2MASS are used to provide additional support for this analysis. Results. We show that there are two very different large-scale triaxial structures coexisting in the in ner Galaxy: a long thin stellar bar constrained to the Galactic plane (|b| < 2 ◦ ) with a position angle of 43. ◦ 0±1. ◦ 8, and a distinct triaxial bulge that extends to at least |b| ≤ 7.5 ◦ with a position angle of 12. ◦ 6±3. ◦ 2. The scale height of the bar source distribution is around 100 pc, whereas for the bulge

The Long Bar in the Milky Way: Corroboration of an Old Hypothesis

Recent Galactic Legacy Infrared Mid-Plane Survey Extraordinaire data have further confirmed the hypothesis of the existence of an in-plane long bar different from the bulge of the Milky Way with the same characteristics as emphasized some years ago by our team. In this paper we present two new analyses that corroborate recent and earlier claims concerning the existence in our Galaxy of a long, flat bar with approximate dimensions of 7.8 kpc ? 1.2 kpc ? 0.2 kpc and a position angle of approximately 43?: (1) star counts with 2MASS All-Sky Data Release and Midcourse Space Experiment data, which give an excess in the plane region along 0? < l < 30? compared with -30? < l < 0? that cannot be due to the bulge, spiral arms, a ring, or extinction; and (2) new data on the distance of the long bar using the red clump method, together with recent observations of our own that are compared with our model and that are in agreement with the long-bar scenario.

A boxy bulge in the Milky Way. Inversion of the stellar statistics equation with 2MASS data

Inverting the stellar statistics equation from 2MASS star counts, we obtain the 3D density distribution of the Galactic bulge as well as its luminosity function in the K-band. This results in a boxy bulge with axial ratios 1:0.5:0.4 and a major axis angle with respect to the Sun-galactic center of 20 ◦ −35 ◦ .

Generation of galactic disc warps due to intergalactic accretion flows onto the disc

The accretion of the intergalactic medium onto the gaseous disc is used to explain the generation of galactic warps. A cup-shaped distortion is expected, due to the transmission of the linear momentum; but, this effect is small for most incident inflow angles and the predominant effect turns out to be the transmission of angular momentum, i.e. a torque giving an integral-sign shaped warp. The torque produced by a flow of velocity ~100 km/s and baryon density ~10^{-25} kg/m^3, which is within the possible values for the intergalactic medium, is enough to generate the observed warps and this mechanism offers quite a plausible explanation. The inferred rate of infall of matter, ~1 M_sun/yr, to the Galactic disc that this theory predicts agrees with the quantitative predictions of chemical evolution resolving key issues, notably the G-dwarf problem. Sanchez-Salcedo (2006) suggests that this mechanism is not plausible because it would produce a dependence of the scaleheight of the disc with the Galactocentric azimuth in the outer disc, but rather than being an objection this is another argument in favour of the mechanism because this dependence is actually observed in our Galaxy.

Searching for the in-plane Galactic bar and ring in DENIS

New evidence for a long thin Galactic bar (in contradistinction to the bulge), as well as for the existence of the ring and the truncation of the inner disc, are sought in the DENIS survey. First, we examine DENIS and Two Micron Galactic Survey star counts for the characteristic signatures of an in-plane bar and ring. The star counts in the plane for

Estimation of Galactic model parameters in high latitudes with 2MASS

30^\circ> l> -30^\circ

Inversion of stellar statistics equation for the Galactic bulge

are shown to be highly asymmetric with considerably more sources at positive than at negative longitudes. At

A catalog of warps in spiral and lenticular galaxies in the Southern hemisphere

|b|\approx 1.5^\circ

Alcock-Paczynski cosmological test

, however, the counts are nearly symmetric. Therefore, the asymmetry is not due to the disc, which is shown to have an inner truncation, or to the bulge, so there has to be another major component in the inner Galaxy that is causing the asymmetries. This component provides up to 50% of the detected sources in the plane between the bulge and