On the Maximum Luminosity of Galaxies and Their Central Black Holes: Feedback From Momentum-Driven Winds

We investigate large-scale galactic winds driven by momentum deposition. Momentum injection is provided by (1) radiation pressure produced by the continuum absorption and scattering of UV photons on dust grains and (2) supernovae. UV radiation can be produced by a starburst or AGN activity. We argue that momentum-driven winds are an efficient mechanism for feedback during the formation of galaxies. We show that above a limiting luminosity, momentum deposition from star formation can expel a significant fraction of the gas in a galaxy. The limiting, Eddington-like luminosity is $L_{\rm M}\simeq(4f_g c/G) \sigma^4$, where $\sigma$ is the galaxy velocity dispersion and $f_g$ is the gas fraction. A starburst that attains $L_{\rm M}$ moderates its star formation rate and its luminosity does not increase significantly further. We argue that ellipticals attain this limit during their growth at $z \gtrsim 1$ and that this is the origin of the Faber-Jackson relation. We show that Lyman break galaxies and ultra-luminous infrared galaxies have luminosities near $L_{\rm M}$. Star formation is unlikely to efficiently remove gas from very small scales in galactic nuclei, i.e., scales much smaller than that of a nuclear starburst. This gas is available to fuel a central black hole (BH). We argue that a BH clears gas out of its galactic nucleus when the luminosity of the BH itself reaches $\approx L_{\rm M}$. This shuts off the fuel supply to the BH and may also terminate star formation in the surrounding galaxy. As a result, the BH mass is fixed to be $M_{\rm BH}\simeq (f_g \kappa_{\rm es}/\pi G^2)\sigma^4$, where $\kappa_{\rm es}$ is the electron scattering opacity. This limit is in accord with the observed $M_{\rm BH}-\sigma$ relation. (Abridged)Comment: 21 pages, emulateapj, accepted to ApJ, minor changes to discussio

Out-of-phase oscillation between superfluid and thermal components for a trapped Bose condensate under oscillatory excitation

The vortex nucleation and the emergence of quantum turbulence induced by oscillating magnetic fields, introduced by Henn E A L, et al. 2009 (Phys. Rev. A 79, 043619) and Henn E A L, et al. 2009 (Phys. Rev. Lett. 103, 045301), left a few open questions concerning the basic mechanisms causing those interesting phenomena. Here, we report the experimental observation of the slosh dynamics of a magnetically trapped $^{87}$Rb Bose-Einstein condensate (BEC) under the influence of a time-varying magnetic field. We observed a clear relative displacement in between the condensed and the thermal fraction center-of-mass. We have identified this relative counter move as an out-of-phase oscillation mode, which is able to produce ripples on the condensed/thermal fractions interface. The out-of-phase mode can be included as a possible mechanism involved in the vortex nucleation and further evolution when excited by time dependent magnetic fields.Comment: 5 pages, 5 figures, 25 reference

Baade's red sheet resolved into stars with HST in the Blue Compact Dwarf Galaxy VII Zw 403

HST WFPC2 observations of the nearby Blue Compact Dwarf Galaxy VII~Zw~403 (= UGC 6456) resolve single stars down to M$_I$$\approx$-2.5, deep enough to identify red giants. This population has a more uniform spatial distribution than the young main-sequence stars and supergiants, forming the structure known as "Baade's red sheet". We conclude that VII~Zw~403 is not a primeval galaxy.Comment: submitted to: ApJ Letter

Stellar Populations Found in the Central kpc of Four Luminous Compact Blue Galaxies at Intermediate Redshift

We investigate the star formation history of the central regions of four Luminous Compact Blue Galaxies (LCBGs). LCBGs are blue (B-V<0.6), compact (MU_B<21.5 mag arcsec^-2) galaxies with absolute magnitudes M_B brighter than -17.5. The LCBGs analyzed here are located at 0.436<z<0.525. They are among the most luminous (M_B < -20.5), blue (B-V < 0.4) and high surface brightness (MU_B < 19.0 mag arcsec^-2) of this population. The observational data used were obtained with the HST/STIS spectrograph, the HST/WF/PC-2 camera and the HST/NICMOS first camera. We find evidence for multiple stellar populations. One of them is identified as the ionizing population, and the other one corresponds to the underlying stellar generation. The estimated masses of the inferred populations are compatible with the dynamical masses, which are typically 2--10x 10^9 M_sun. Our models also indicate that the first episodes of star formation the presented LCBGs underwent happened between 5 and 7 Gyr ago. We compare the stellar populations found in LCBGs with the stellar populations present in bright, local HII galaxies, nearby spheroidal systems and Blue Compact Dwarf Galaxies. It turns out that the underlying stellar populations of LCBGs are similar yet bluer to those of local HII galaxies. It is also the case that the passive color evolution of the LCBGs could convert them into local Spheroidal galaxies if no further episode of star formation takes place. Our results help to impose constraints on evolutionary scenarios for the population of LCBGs found commonly at intermediate redshifts.Comment: 35 pages, 10 Figures. Accepted for publication in AJ. Compile with pdflatex. Contains png figure