Discovery of Multi-Phase Cold Accretion in a Massive Galaxy at z=0.7

We present detailed photo+collisional ionization models and kinematic models of the multi-phase absorbing gas, detected within the HST/COS, HST/STIS, and Keck/HIRES spectra of the background quasar TON 153, at 104 kpc along the projected minor axis of a star-forming spiral galaxy (z=0.6610). Complementary g'r'i'Ks photometry and stellar population models indicate that the host galaxy is dominated by a 4 Gyr stellar population with slightly greater than solar metallicity and has an estimated log(M*)=11 and a log(Mvir)=13. Photoionization models of the low ionization absorption, (MgI, SiII, MgII and CIII) which trace the bulk of the hydrogen, constrain the multi-component gas to be cold (logT=3.8-5.2) and metal poor (-1.68<[X/H]<-1.64). A lagging halo model reproduces the low ionization absorption kinematics, suggesting gas coupled to the disk angular momentum, consistent with cold accretion mode material in simulations. The CIV and OVI absorption is best modeled in a separate collisionally ionized metal-poor (-2.50<[X/H]<-1.93) warm phase with logT=5.3. Although their kinematics are consistent with a wind model, given the 2-2.5dex difference between the galaxy stellar metallicity and the absorption metallicity indicates the gas cannot arise from galactic winds. We discuss and conclude that although the quasar sight-line passes along the galaxy minor axis at projected distance of 0.3 virial radii, well inside its virial shock radius, the combination of the relative kinematics, temperatures, and relative metallicities indicated that the multi-phase absorbing gas arises from cold accretion around this massive galaxy. Our results appear to contradict recent interpretations that absorption probing the projected minor axis of a galaxy is sampling winds.Comment: 16 pages, 11 figures, accepted for publication in MNRA

H-alpha Imaging with HST+NICMOS of An Elusive Damped Ly-alpha Cloud at z=0.6

Despite previous intensive ground-based imaging and spectroscopic campaigns and wide-band HST imaging of the z=0.927 QSO 3C336 field, the galaxy that hosts the damped Ly-alpha system along this line-of-sight has eluded detection. We present a deep narrow-band H-alpha image of the field of this z=0.656 damped Ly-alpha absorber, obtained through the F108N filter of NICMOS 1 onboard the Hubble Space Telescope. The goal of this project was to detect any H-alpha emission 10 times closer than previous studies to unveil the damped absorber. We do not detect H-alpha emission between 0.05'' and 6'' (0.24 and 30 $h^{-1}$ kpc) from the QSO, with a 3-sigma flux limit of $3.70 \times 10^{-17} h^{-2}$ erg/s/cm^2 for an unresolved source, corresponding to a star formation rate (SFR) of $0.3 h^{-2}$ M_sun/yr. This leads to a 3-sigma upper limit of 0.15 M_sun/yr/kpc^2 on the SFR density, or a maximum SFR of 1.87 M_sun/yr assuming a disk of 4 kpc in diameter. This result adds to the number of low redshift damped Ly-alpha absorbers that are not associated with the central regions of Milky-Way-like disks. Damped Ly-alpha absorption can arise from high density concentrations in a variety of galactic environments including some that, despite their high local HI densities, are not conducive to widespread star formation.Comment: 18 pages, 3 figures. Replaced to match published version in ApJ, 550, 585 (Apr 1 2001

High Resolution STIS/HST and HIRES/Keck Spectra of Three Weak MgII Absorbers Toward PG 1634+706

High resolution optical (HIRES/Keck) and UV (STIS/HST) spectra, covering a large range of chemical transitions, are analyzed for three single-cloud weak MgII absorption systems along the line of sight toward the quasar PG 1634+706. Weak MgII absorption lines in quasar spectra trace metal-enriched environments that are rarely closely associated with the most luminous galaxies (>0.05L^*). The two weak MgII systems at z=0.81 and z=0.90 are constrained to have >=solar metallicity, while the metallicity of the z=0.65 system is not as well-constrained, but is consistent with >1/10th solar. These weak MgII clouds are likely to be local pockets of high metallicity in a lower metallicity environment. All three systems have two phases of gas, a higher density region that produces narrower absorption lines for low ionization transitions, such as MgII, and a lower density region that produces broader absorption lines for high ionization transitions, such as CIV. The CIV profile for one system (at z=0.81) can be fit with a single broad component (b~10 km/s), but those for the other two systems require one or two additional offset high ionization clouds. Two possible physical pictures for the phase structure are discussed: one with a low-ionization, denser phase embedded in a lower density surrounding medium, and the other with the denser clumps surrounding more highly ionized gas.Comment: 32 pages, 4 figures; to appear in ApJ on May 20, 200

The Absorption Signatures of Dwarf Galaxies: The z=1.04 Multicloud Weak MgII Absorber toward PG 1634+706

We analyze high resolution spectra of a multi--cloud weak [defined as W_r(MgII) < 0.3 A] absorbing system along the line of sight to PG 1634+706. This system gives rise to a partial Lyman limit break and absorption in MgII, SiII, CII, SiIII, SiIV, CIV, and OVI. The lower ionization transitions arise in two kinematic subsystems with a separation of ~150 km/s. Each subsystem is resolved into several narrow components, having Doppler widths of 3-10 kms. For both subsystems, the OVI absorption arises in a separate higher ionization phase, in regions dominated by bulk motions in the range of 30-40 km/s. The two OVI absorption profiles are kinematically offset by ~50 km/s with respect to each of the two lower ionization subsystem. In the stronger subsystem, the SiIII absorption is strong with a distinctive, smooth profile shape and may partially arise in shock heated gas. Moreover, the kinematic substructure of SiIV traces that of the lower ionization MgII, but may be offset by ~3 km/s. Based upon photoionization models, constrained by the partial Lyman limit break, we infer a low metallicity of ~0.03 solar for the low ionization gas in both subsystems. The broader OVI phases have a somewhat higher metallicity, and they are consistent with photoionization; the profiles are not broad enough to imply production of OVI through collisional ionization. Various models, including outer disks, dwarf galaxies, and superwinds, are discussed to account for the phase structure, metallicity, and kinematics of this absorption system. We favor an interpretation in which the two subsystems are produced by condensed clouds far out in the opposite extremes of a multi-layer dwarf galaxy superwind

Far-off-resonant wave interaction in one-dimensional photonic crystals with quadratic nonlinearity

We extend a recently developed Hamiltonian formalism for nonlinear wave interaction processes in spatially periodic dielectric structures to the far-off-resonant regime, and investigate numerically the three-wave resonance conditions in a one-dimensional optical medium with $\chi^{(2)}$ nonlinearity. In particular, we demonstrate that the cascading of nonresonant wave interaction processes generates an effective $\chi^{(3)}$ nonlinear response in these systems. We obtain the corresponding coupling coefficients through appropriate normal form transformations that formally lead to the Zakharov equation for spatially periodic optical media.Comment: 14 pages, 4 figure

Mg II Absorber Number Density at z~0.05: Implications for Omega_DLA Evolution

An unbiased sample of 147 quasar/AGN spectra, obtained with the FOS/HST, has been searched for intervening MgII absorbers over the redshift range 0<z<0.15. The total redshift path searched is 18.8, with the survey being 80% complete to a 5-sigma rest-frame equivalent width, W_r(2796), of 0.6 Ang. Main results of this work are: [1] Four systems were found, with a mean redshift of =0.06, yielding a redshift number density dN/dz=0.22(+0.12)(-0.09) for absorbers with W_r(2796)>0.6 Ang. This is consistent with the value expected if these systems do not evolve from higher redshifts (z=2.2). [2] No systems with W_r(2796)<0.6 Ang were found. It is a 2-sigma result to have a null detection of smaller W_r(2796) systems. If this implies a turnover in the low W_r(2796) region of the equivalent width distribution at z~0, then there is at least a 25% reduction in the average galaxy gas cross section from z<0.2 galaxies. [3] These systems have strong FeII absorption and are good candidates for damped Ly-alpha absorbers DLAs (see Rao & Turnshek 2000, ApJS, 130, 1). This translates to a redshift number density of dN/dz=0.08(+0.09)(-0.05) for DLAs at z~0. In tandem with the data analyzed by Rao & Turnshek, these results indicate that the redshift number density of DLAs does not evolve from z~4 to z~0. If the HI mass function does not evolve from z~0.5 to z~0, then the cosmological HI mass density is also deduced to not evolve from z~4 to z~0. These z~0 results for MgII absorption-selected DLAs are at odds with those based upon 21-cm emission from HI galaxies by a factor of five to six.Comment: 23 pages, 7 Figures, accepted to ApJ. Replaced version includes additional figures and tables and substantial modifications to the tex