We present the stellar kinematics in the central 2 ′′ of the luminous elliptical galaxy M87 (NGC 4486), using laser adaptive optics to feed the Gemini telescope integral-field spectrograph, NIFS. The velocity dispersion rises to 480 km s −1 at 0.2 ′′ . We combine these data with extensive stellar kinematics out to large radii to derive a blackhole mass equal to (6.6 ± 0.4) × 10 9 M ⊙ , using orbit-based axisymmetric models and including only the NIFS data in the central region. Including previously-reported ground-based data in the central region drops the uncertainty to 0.25 × 10 9 M ⊙ with no change in the best-fit mass; however, we rely on the values derived from the NIFS-only data in the central region in order to limit systematic differences. The best-fit model shows a significant increase in the tangential velocity anisotropy of stars orbiting in the central region with decreasing radius; similar to that seen in the centers of other core galaxies. The black-hole mass is insensitive to the inclusion of a dark halo in the models -the high angular-resolution provided by the adaptive optics breaks the degeneracy between black-hole mass and stellar mass-to-light ratio. The present black-hole mass is in excellent agreement with the Gebhardt & Thomas value, implying that the dark halo must be included when the kinematic influence of the black hole is poorly resolved. This degeneracy implies that the black-hole masses of luminous core galaxies, where this effect is important, may need to be re-evaluated. The present value exceeds the prediction of the black hole-dispersion and black hole-luminosity relations, both of which predict about 1 × 10 9 M ⊙ for M87, by close to twice the intrinsic scatter in the relations. The high-end of the black hole correlations may be poorly determined at present.

We investigate the relation between the star formation rate surface density (Σ SF R ) and the mass surface density of gas (Σ gas ) in NGC 5194 (a.k.a. M51a, Whirlpool Galaxy). VIRUS-P integral field spectroscopy of the central 4.1 × 4.1 kpc 2 of the galaxy is used to measure Hα, Hβ, [NII]λλ6548,6584, and [SII]λλ6717,6731 emission line fluxes for 735 regions ∼170 pc in diameter. We use the Balmer decrement to calculate nebular dust extinctions, and correct the observed fluxes in order to measure accurately Σ SF R in each region. Archival HI 21cm and CO maps with similar spatial resolution to that of VIRUS-P are used to measure the atomic and molecular gas surface density for each region. We present a new method for fitting the Star Formation Law (SFL), which includes the intrinsic scatter in the relation as a free parameter, allows the inclusion of non-detections in both Σ gas and Σ SF R , and is free of the systematics involved in performing linear correlations over incomplete data in logarithmic space. After rejecting regions whose nebular spectrum is affected by the central AGN in NGC 5194, we use the [SII]/Hα ratio to separate spectroscopically the contribution from the diffuse ionized gas (DIG) in the galaxy, which has a different temperature and ionization state from those of H II regions in the disk. The DIG only accounts for 11% of the total Hα luminosity integrated over the whole central region, but on local scales it can account for up to a 100% of the Hα emission, especially in the inter-arm regions. After removing the DIG contribution from the Hα fluxes, we measure a slope N = 0.82±0.05, and an intrinsic scatter ǫ = 0.43 ± 0.02 dex for the molecular gas SFL. We also measure a typical depletion timescale τ = Σ HI+H2 /Σ SF R ≈ 2 Gyr, in good agreement with recent measurements by Bigiel et al. (2008). The atomic gas density shows no correlation with the SFR, and the total gas SFL in the sampled density range closely follows the molecular gas SFL. Integral field spectroscopy allows a much cleaner measurement of Hα emission line fluxes than narrow-band imaging, since it is free of the systematics introduced by continuum subtraction, underlying photospheric absorption, and contamination by the [NII] doublet. We assess the validity of different corrections usually applied in narrow-band measurements to overcome these issues and find that while systematics are introduced by these corrections, they are only dominant in the low surface brightness regime. The disagreement with the previous measurement of a super-linear molecular SFL by Kennicutt et al. (2007) is most likely due to differences in the fitting method. Our results support the recent evidence for a low, and close to constant, star formation efficiency (SFE=τ −1 ) in the molecular component of the ISM. The data shows an excellent agreement with the recently proposed model of the SFL by Krumholz et al. (2009b). The large intrinsic scatter observed may imply the existence of other parameters, beyond the availability of gas, which are important at settin...

We study the escape of Lyα photons from Lyα emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 < z < 3.8 detected through integral-field spectroscopy of blank fields by the HETDEX Pilot Survey. For 89 LAEs with broad-band counterparts we measure UV luminosities and UV slopes, and estimate E(B − V ) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SF R). Comparison between the observed Lyα luminosity and -2 -that predicted by the dust-corrected SF R yields the Lyα escape fraction. We also measure the Lyα luminosity function and luminosity density (ρ Lyα ) at 2 < z < 4. Using this and other measurements from the literature at 0.3 < z < 7.7 we trace the redshift evolution of ρ Lyα . We compare it to the expectations from the starformation history of the universe and characterize the evolution of the Lyα escape fraction of galaxies. LAEs at 2 < z < 4 selected down to a luminosity limit of L(Lyα) > 3 − 6 × 10 42 erg s −1 (0.25 to 0.5 L * ), have a mean E(B − V ) = 0.13 ± 0.01, implying an attenuation of ∼ 70% in the UV. They show a median UV uncorrected SF R = 11 M ⊙ yr −1 , dust-corrected SF R = 34 M ⊙ yr −1 , and Lyα equivalent widths (EW s) which are consistent with normal stellar populations. We measure a median Lyα escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Lyα escape fraction in LAEs correlates with E(B − V ) in a way that is expected if Lyα photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Lyα EW with dust, due to a clumpy multi-phase ISM, is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Lyα can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Lyα escape fraction of LAEs from z ∼ 4 to 2. We see hints of a drop in the number density of LAEs from z ∼ 4 to 2 in the redshift distribution and the Lyα luminosity function, although larger samples are required to confirm this. The mean Lyα escape fraction of the overall galaxy population decreases significantly from z ∼ 6 to z ∼ 2. Our results point towards a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z ∼ 6 and 2, reducing their Lyα escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Lyα photons is reached by z ∼ 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.

We present the results of Keck/NIRSPEC spectroscopic observations of three Lyα emitting galaxies (LAEs) at z ∼ 2.3 discovered with the HETDEX pilot survey. We detect Hα, [O III], and Hβ emission from two galaxies at z = 2.29 and 2.49, designated HPS194 and HPS256, respectively, representing the first detection of multiple rest-frame optical emission lines in galaxies at high-redshift selected on the basis of their Lyα emission. We find that the redshifts of the Lyα emission from these galaxies are offset redward of the systemic redshifts (derived from the Hα and [O III] emission) by ∆v = 162 ± 37 (photometric) ± 42 (systematic) km s −1 for HPS194, and ∆v = 36 ± 35 ± 18 km s −1 for HPS256. An interpretation for HPS194 is that a large-scale outflow may be occurring in its interstellar medium. This outflow is likely powered by star-formation activity, as examining emission line ratios implies that neither LAE hosts an active galactic nucleus. Using the upper limits on the [N II] emission we place meaningful constraints on the gas-phase metallicities in these two LAEs of Z < 0.17 and < 0.28 Z ⊙ (1σ). Measuring the stellar masses of these objects via spectral energy distribution fitting (∼ 10 10 and 6 × 10 8 M ⊙ , respectively), we study the nature of LAEs in a mass-metallicity plane. At least one of these two LAEs appears to be more metal poor than continuum-selected star-forming galaxies at the same redshift and stellar mass, implying that objects exhibiting Lyα emission may be systematically less chemically enriched than the general galaxy population. We use the spectral energy distributions of these two galaxies to show that neglecting the contribution of the measured emission line fluxes when fitting stellar population models to the observed photometry can result in overestimates of the population age by orders of magnitude, and the stellar mass by a factor of ∼ 2. This effect is particularly important at z 7, where similarly strong emission lines may masquerade in the photometry as a 4000 Å break.

We present new constraints on the density profiles of dark matter (DM) halos in seven nearby dwarf galaxies from measurements of their integrated stellar light and gas kinematics. The gas kinematics of low mass galaxies frequently suggest that they contain constant density DM cores, while N-body simulations instead predict a cuspy profile. We present a data set of high resolution integral field spectroscopy on seven galaxies and measure the stellar and gas kinematics simultaneously. Using Jeans modeling on our full sample, we examine whether gas kinematics in general produce shallower density profiles than are derived from the stars. Although 2/7 galaxies show some localized differences in their rotation curves between the two tracers, estimates of the central logarithmic slope of the DM density profile, γ, are generally robust. The mean and standard deviation of the logarithmic slope for the population are γ = 0.67 ± 0.10 when measured in the stars and γ = 0.58 ± 0.24 when measured in the gas. We also find that the halos are not under-concentrated at the radii of half their maximum velocities. Finally, we search for correlations of the DM density profile with stellar velocity anisotropy and other baryonic properties. Two popular mechanisms to explain cored DM halos are an exotic DM component or feedback models that strongly couple the energy of supernovae into repeatedly driving out gas and dynamically heating the DM halos. While such models do not yet have falsifiable predictions that we can measure, we investigate correlations that may eventually be used to test models. We do not find a secondary parameter that strongly correlates with the central DM density slope, but we do find some weak correlations. The central DM density slope weakly correlates with the abundance of α elements in the stellar population, anti-correlates with HI fraction, and anti-correlates with vertical orbital anisotropy. We expect, if anything, the opposite of these three trends for feedback models. Determining the importance of these correlations will require further model developments and larger observational samples.