Browsing by Subject "ultraluminous infrared galaxies"

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Dissipation and Extra Light in Galactic Nuclei. II. "Cusp" Ellipticals
(2009-03) Hopkins, Philip F.; Cox, Thomas J.; Dutta, Suvendra N.; Hernquist, Lars; Kormendy, John; Lauer, Tod R.; Kormendy, John
We study the origin and properties of "extra" or "excess" central light in the surface brightness profiles of cusp or power-law elliptical galaxies. Dissipational mergers give rise to two-component profiles: an outer profile established by violent relaxation acting on stars already present in the progenitor galaxies prior to the final stages of the merger, and an inner stellar population comprising the extra light, formed in a compact central starburst. By combining a large set of hydrodynamical simulations with data that span a broad range of profiles at various masses, we show that observed cusp ellipticals appear consistent with the predicted "extra light" structure, and we use our simulations to motivate a two-component description of the observations that allows us to examine how the properties and mass of this component scale with, e. g., the mass, gas content, and other properties of the galaxies. We show how to robustly separate the physically meaningful extra light and outer, violently relaxed profile, and demonstrate that the observed cusps and "extra light" are reliable tracers of the degree of dissipation in the spheroid-forming merger. We show that the typical degree of dissipation is a strong function of stellar mass, roughly tracing the observed gas fractions of disks of the same mass over the redshift range z similar to 0-2. We demonstrate a correlation between the strength of this component and effective radius at fixed mass, in the sense that systems with more dissipation are more compact, sufficient to explain the discrepancy in the maximum phase-space and mass densities of ellipticals and their progenitor spirals. We show that the outer shape of the light profile in simulated and observed systems (when fit to properly account for the central light) does not depend on mass, with a mean outer Sersic index similar to 2.5. We also explore how this relates to, e. g., the shapes, kinematic properties, and stellar population gradients of ellipticals. Extra light contributes to making remnants rounder and diskier, and imprints stellar population gradients. Simulations with the gas content needed to match observed surface brightness profiles reproduce the observed age, metallicity, and color gradients of cusp ellipticals, and we make predictions for how these can be used as tracers of the degree of dissipation in spheroid Formation.
Feedback In Luminous Obscured Quasars
(2011-05) Greene, Jenny E.; Zakamska, Nadia L.; Ho, Luis C.; Barth, Aaron J.; Greene, Jenny E.
We use spatially resolved long-slit spectroscopy from Magellan to investigate the extent, kinematics, and ionization structure in the narrow-line regions of 15 luminous, obscured quasars with z < 0.5. Increasing the dynamic range in luminosity by an order of magnitude, as well as improving the depth of existing observations by a similar factor, we revisit relations between narrow-line region size and the luminosity and linewidth of the narrow emission lines. We find a slope of 0.22 +/- 0.04 for the power-law relationship between size and luminosity, suggesting that the nebulae are limited by availability of gas to ionize at these luminosities. In fact, we find that the active galactic nucleus is effectively ionizing the interstellar medium over the full extent of the host galaxy. Broad (similar to 300-1000 km s(-1)) linewidths across the galaxies reveal that the gas is kinematically disturbed. Furthermore, the rotation curves and velocity dispersions of the ionized gas remain constant out to large distances, in striking contrast to normal and starburst galaxies. We argue that the gas in the entire host galaxy is significantly disturbed by the central active galactic nucleus. While only similar to 10(7)-10(8) M-circle dot worth of gas are directly observed to be leaving the host galaxies at or above their escape velocities, these estimates are likely lower limits because of the biases in both mass and outflow velocity measurements and may in fact be in accord with expectations of recent feedback models. Additionally, we report the discovery of two dual obscured quasars, one of which is blowing a large-scale (similar to 10 kpc) bubble of ionized gas into the intergalactic medium.
Less Than 10 Percent Of Star Formation In Z Similar To 0.6 Massive Galaxies Is Triggered By Major Interactions
(2009-10) Robaina, Aday R.; Bell, Eric F.; Skelton, Rosalind E.; McIntosh, Daniel H.; Somerville, Rachel S.; Zheng, Xianzhong; Rix, Hans-Walter; Bacon, David; Balogh, Michael; Barazza, Fabio D.; Barden, Marco; Boehm, Asmus; Caldwell, John A. R.; Gallazzi, Anna; Gray, Meghan E.; Haeussler, Boris; Heymans, Catherine; Jahnke, Knud; Jogee, Shardha; van Kampen, Eelco; Lane, Kyle; Meisenheimer, Klaus; Papovich, Casey; Peng, Chien Y.; Sanchez, Sebastian F.; Skibba, Ramin; Taylor, Andy; Wisotzki, Lutz; Wolf, Christian; Jogee, Shardha
Both observations and simulations show that major tidal interactions or mergers between gas-rich galaxies can lead to intense bursts of star formation. Yet, the average enhancement in star formation rate (SFR) in major mergers and the contribution of such events to the cosmic SFR are not well estimated. Here we use photometric redshifts, stellar masses, and UV SFRs from COMBO-17, 24 mu m SFRs from Spitzer, and morphologies from two deep Hubble Space Telescope (HST) cosmological survey fields (ECDFS/GEMS and A901/STAGES) to study the enhancement in SFR as a function of projected galaxy separation. We apply two-point projected correlation function techniques, which we augment with morphologically selected very close pairs (separation <2 '') and merger remnants from the HST imaging. Our analysis confirms that the most intensely star-forming systems are indeed interacting or merging. Yet, for massive (M(*) >= 10(10) M(circle dot)) star-forming galaxies at 0.4 < z < 0.8, we find that the SFRs of galaxies undergoing a major interaction (mass ratios <= 1:4 and separations <= 40 kpc) are only 1.80 +/- 0.30 times higher than the SFRs of non-interacting galaxies when averaged over all interactions and all stages of the interaction, in good agreement with other observational works. Our results also agree with hydrodynamical simulations of galaxy interactions, which produce some mergers with large bursts of star formation on similar to 100 Myr timescales, but only a modest SFR enhancement when averaged over the entire merger timescale. We demonstrate that these results imply that only less than or similar to 10% of star formation at 0.4 <= z <= 0.8 is triggered directly by major mergers and interactions; these events are not important factors in the build-up of stellar mass since z = 1.
The Mid-Infrared Narrow-Line Baldwin Effect Revealed By Spitzer
(2009-01) Keremedjiev, Mark; Hao, Lei; Charmandaris, Vassilis; Hao, Lei
We present our discovery of a narrow-line Baldwin effect, an anticorrelation between the equivalent width (EW) of a line and the flux of the associated continuum, in 5-20 mu m mid-infrared (mid-IR) lines from a sample of 68 active galactic nuclei (AGNs), located at z < 0.5, observed with the Infrared Spectrograph on the Spitzer Space Telescope. Our analysis reveals a clear anticorrelation between the EW of the [S IV] 10.51 mu m, [Ne II] 12.81 mu m, and [Ne III] 15.56 mu m lines and their mid-IR continuum luminosities, while the Baldwin effect for [Ne v] 14.32 mu m is not as obvious. We suggest that this anticorrelation is driven by the central AGN, and not circumnuclear star formation in the host galaxy, and present a new method of analyzing this effect in mid-IR lines. We also find that the slope of the narrow-line Baldwin effect in the mid-IR does not appear to steepen with increasing ionization potential. Examining the dependence of the EW on the Eddington ratio (L/L(Edd)), we find no strong relationship for mid-IR lines. Our study indicates that the narrow-line mid-IR Baldwin effect is quite different from the broad-line optical/UV Baldwin effect, and it is possible that the two effects are unrelated. The anticorrelations discovered open new possibilities in understanding the physics of the ionizing region and the continuum reprocessing by dust.
Millimeter Observations Of A Sample Of High-Redshift Obscured Quasars
(2009-11) Martinez-Sansigre, Alejo; Karim, Alexander; Schinnerer, Eva; Omont, Alain; Smith, Daniel J. B.; Wu, Jingwen; Hill, Gary J.; Klockner, Hans-rainer; Lacy, Mark; Rawlings, Steve; Willott, Chris J.; Hill, Gary J.
We present observations at 1.2 mm with Max-Planck Millimetre Bolometer Array (MAMBO-II) of a sample of z greater than or similar to 2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. The typical rms noise achieved by the MAMBO observations is 0.55 mJy beam(-1) and five out of 21 sources (24%) are detected at a significance of >= 3 sigma. Stacking all sources leads to a statistical detection of < S(1.2 mm)> = 0.96 +/- 0.11 mJy and stacking only the non-detections also yields a statistical detection, with < S(1.2 mm)> = 0.51 +/- 0.13 mJy. At the typical redshift of the sample, z = 2, 1 mJy corresponds to a far-infrared luminosity L(FIR) similar to 4 x 10(12) L(circle dot). If the far-infrared luminosity is powered entirely by star formation, and not by active galactic nucleus heated dust, then the characteristic inferred star formation rate is similar to 700 M(circle dot) yr(-1). This far-infrared luminosity implies a dust mass of M(d) similar to 3 x 10(8) M(circle dot), which is expected to be distributed on similar to kpc scales. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. Combining our observations at 1.2 mm with mid-and far-infrared data, and additional observations for two objects at 350 mu m using SHARC-II, we present dust spectral energy distributions (SEDs) for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. This additional extinction can be consistently achieved by the mass of cool dust responsible for the far-infrared emission, provided the bulk of the dust is within a radius similar to 2-3 kpc. Comparison of our sample to other samples of z similar to 2 quasars suggests that obscured quasars have, on average, higher far-infrared luminosities than unobscured quasars. There is a hint that the host galaxies of obscured quasars must have higher cool-dustmasses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z = 2.767, we detect the CO(3-2) transition, with S(CO)Delta nu = 630 +/- 50 mJy km s(-1), corresponding to L(CO(3-2)) = 3.2 x 10(7) L(circle dot), or a brightness-temperature luminosity of L'(CO(3-2)) = 2.4 x 10(10) K km s(-1) pc(2). For another source at z = 4.17, the lack of detection of the CO(4-3) line suggests the line to have a brightness-temperature luminosity L'(CO(4-3)) < 1 x 10(10) K km s(-1) pc(2). Under the assumption that in these objects the high-J transitions are thermalized, we can estimate the molecular gas contents to be M(II2) = 1.9 x 10(10) M(circle dot) and < 8 x 10(9) M(circle dot), respectively. The estimated gas depletion timescales are tau(g) = 4 Myr and <16 Myr, and low gas-to-dust mass ratios of M(g)/M(d) = 19 and <20 are inferred. These values are at the low end but consistent with those of other high-redshift galaxies.
A Spitzer High-Resolution Mid-Infrared Spectral Atlas of Starburst Galaxies
(2009-10) Bernard-Salas, J.; Spoon, H. W. W.; Charmandaris, V.; Lebouteiller, V.; Farrah, D.; Devost, D.; Brandl, B. R.; Wu, Y. L.; Armus, L.; Hao, L.; Sloan, G. C.; Weedman, D.; Houck, J. R.; Hao, L.
We present an atlas of Spitzer/IRS high-resolution (R similar to 600) 10-37 mu m spectra for 24 well known starburst galaxies. The spectra are dominated by fine-structure lines, molecular hydrogen lines, and emission bands of polycyclic aromatic hydrocarbons (PAHs). Six out of the eight objects with a known active galactic nucleus (AGN) component show emission of the high excitation [Ne v] line. This line is also seen in one other object (NGC 4194) with, a priori, no known AGN component. In addition to strong PAH emission features in this wavelength range (11.3, 12.7, 16.4 mu m), the spectra reveal other weak hydrocarbon features at 10.6, 13.5, 14.2 mu m, and a previously unreported emission feature at 10.75 mu m. An unidentified absorption feature at 13.7 mu m is detected in many of the starbursts. We use the fine-structure lines to derive the abundance of neon and sulfur for 14 objects where the Hi 7-6 line is detected. We further use the molecular hydrogen lines to sample the properties of the warm molecular gas. Several basic diagrams characterizing the properties of the sample are also shown. We have combined the spectra of all the pure starburst objects to create a high signal-to-noise ratio template, which is available to the community.