THE GALEX EXTRAGALACTIC SPECTRA DATA BASE

Abstract: 

 
We have matched objects in the Galaxy Evolution Explorer (GALEX) spectroscopic fields with publicly available ultraviolet, optical, and infrared surveys, to construct a photometric and spectroscopic catalog for non-stellar objects with GALEX spectroscopic counterparts. Of the total sample of GALEX spectra recorded in the database, approximately 20\% are determined to reliably correspond to non-stellar objects. These objects have been cross-matched with SDSS, WISE, and 2MASS photometric and spectroscopic survey catalogs, and VISTA and UKIRT near-IR catalogs where available, to construct spectral energy distributions (SED's) from the GALEX-FUV to WISE-w4 magnitudes for all non-stellar objects within the fields. Analysis of 209 fields with at least one object matched in SDSS give a total of 12,020 extragalactic objects, comprising 1974 known QSOs and AGNs, 2274 star-forming galaxies, 6327 quiescent spiral galaxies, and 386 elliptical galaxies.

TBA

Molecular gas properties in young stellar clusters with a suppressed star cluster wind

In extremely compact and dense star-forming clouds a global star cluster wind could be suppressed. In this case the stellar feedback is unable to expel the leftover gas from the cluster. Young massive stars remain embedded into a dense residual gas and stir it moving in the gravitational well of the system. I shall present a self-consistent model for the molecular gas distribution in such young, enshrouded stellar clusters. It is assumed that the cloud collapse has been terminated and the star formation ceased when a balance between the turbulent pressure and gravity and between the turbulent energy dissipation and regeneration rates has been established. These conditions result in an equation that determines the residual gas density distribution that, in turn, allows one to obtain other characteristics of the leftover gas and the star formation efficiency. Finally, I shall confront this model with D1 molecular cloud and its embedded cluster in the dwarf spheroidal galaxy NGC 5253.

Reverberation mapping black hole accretion flows

Most of the power from an Active Galactic Nucleus is released close to the black hole, and thus studying the inner accretion flow, at the intersection of inflow and outflow, is essential for understanding how black holes grow and affect galaxy evolution. In the past decade, we have had a breakthrough in how we probe the inner accretion flow, through the discovery of X-ray Reverberation Mapping, where X-rays produced close to the black hole reverberate off inflowing gas. By measuring reverberation time delays, we can quantify the effects of strongly curved space time and the black hole spin, which is key for understanding how efficiently energy can be tapped from the accretion process. In this talk, I will give an overview of this field, and show how extending these spectral-timing techniques to transient accretion events like Tidal Disruption Events and black hole X-ray binaries is helping us probe the formation of X-ray coronae, jets and other relativistic outflows.

Title: THE ROLE OF SHOCKS IN THE EMISSION OF THE SINGLY IONIZED CARBON  IN GALAXIES

SUMMARY:

The fine structure [CII] line at 157.7um is considered a good tracer of star formation because it is unaffected by dust attenuation and it is bright enough to be detected in high-z galaxies. This happens because the singly ionized carbon C+ collisionally excited by the surrounding neutral atomic and molecular hydrogen acts as the main coolant for the molecular clouds heated by young bright stars in galaxies. In this talk I will present a few cases of nearby galaxies where shocks are instead the reason for the [CII] emission. In particular I will talk about galaxies where jets from the central AGN affect the interstellar medium at great distance from the nucleus and about a few other cases where shocks from galaxy interactions are at the origin of a [CII] emission excess.

Cometary emission processes: fingerprints of their physical and chemical behavior

I will discuss key atomic and molecular processes in cometary atmospheres.  Like comets in our solar system, it will be difficult if not impossible to directly study the physical and chemical properties of comets around other stars. Instead, we have to infer these properties from the gas and dust surrounding them. Atomic and molecular reaction such as dissociation, ionization, and charge exchange both alter gases surrounding comets. Because many reactions result in the emission of light, they also offer insight into the composition and radiation environment exocomets are exposed to. In this presentation I will provide a broad review of radiative processes in cometary atmospheres, with a particular focus on spectral modeling, observational opportunities, and anticipated challenges in the interpretation of new observations, based on our current understanding of the atomic and molecular processes occurring in the atmospheres of small, icy bodies. Close to the surface, comet atmospheres form a thermalized atmosphere tracing the irregular shape of the nucleus. Gravity is too low to retain the gas, which flows out to form a large collisionless exosphere. As such, cometary comae represent conditions that are both familiar, as well as unattainable in laboratories on Earth, necessitating state-of-the-art theoretical treatments of the relevant microphysical processes. Radiative processes offer direct diagnostics of the local conditions, as well as the macroscopic coma properties. Finally, measurements of cometary compositions are uniquely valuable because they provide information on the formation and evolution of our solar system, but extracting chemical abundances from spectroscopic measurements of the coma requires detailed models that span a broad range of physical regimes (both macroscopic and microscopic).

Black hole accretion flows: from nearby stellar binaries to quasars at cosmic dawn

Accretion onto black holes transforms the darkest objects in the universe into the brightest. I will review what we know about the emission from the accretion flow, starting with the stellar mass black holes in binary systems in our own galaxy. Scaling up to the supermassive black holes in active galaxies and quasars reveals both similarities and differences. One of the key similarities is the 'changing look' phenomena in active galaxies, where the UV continuum associated with an optically thick accretion flow drops over a few months/years, triggering the disappearance of the characteristic broad emission lines, analogous to the state transition in binaries. One of the key differences is the nature of the accretion flow above the transition luminosity, where the stellar mass black holes look like standard discs and have variability timescales like standard discs while the supermassive ones do not. Only at the highest luminosities (extreme narrow line Seyfert 1 galaxies and the weak line quasars) does the accretion flow match to the disc models. I will speculate on the physics underlying all the behavior, and give a united picture of the accretion flow.

The gas-phase metallicity and ionization parameter are two primary parameters that drive the variations of emission line spectra in HII regions. There is an increasing amount of evidence that these two parameters are correlated. Theoretical works on the dynamical evolution of HII regions predict an anti-correlation between metallicity and ionization parameter. However, observations of HII region spectra have yielded a variety of different correlations, including anti-correlations, positive correlations, and even no correlation. All these measurements of the correlation rely on photoionization modeling. Also, different combinations of emission lines are used for calibrating metallicity and ionization parameter in different works. To solve the above problem, we examine how the derived correlation between metallicity and ionization parameter depends on the choice of models and emission lines. In this talk, I will show that it is important to constrain the model parameters using observational data before making any measurement. With the MaNGA IFU data, we compute a best-fit photoionization model for general HII regions and use a Bayesian method to fit metallicities and ionization parameters simultaneously. Our result shows that a positive correlation exists between the gas-phase metallicity and ionization parameter, regardless of which combination of emission lines is used for the fitting. This result clearly contradicts the prediction by the dynamical model. I will discuss potential mechanisms that lead to this discrepancy, and how it might be solved with future IFU surveys on HII regions.

The fifth incarnation of the Sloan Digital Sky Survey (SDSS-V) began taking data last year and is in the process of transitioning to the use of a robotic positioning system. I will described the SDSS-V Milky Way Mapper program and its goals. The first of its major goals is to understand the history and structure of the Milky Way. Following upon work done with the APOGEE-1 and 2 surveys the Milky Way Mapper will use approximately 6 million stars to trace out the detailed structure of the Galaxy. The second major goal is to understand stellar astrophysics. The Milky Way Mapper contains several smaller programs called cartons, whose goals cover a wide variety of stellar candidates including white dwarfs, binary stars, young stellar objects, planet hosts, asteroseismology targets and x-ray binaries. These cartons will allow us to explore all sorts of interesting topics that can only be done with a large-scale spectroscopic survey. I will give updates on the current progress of the survey, and lay out our plans for the future.

The deaths of massive stars seed our universe with black holes and neutron stars - the most exotic objects of the stellar graveyard. The births of these stellar remnants, as well as their mergers when paired in binaries, power explosions that can launch the most relativistic jets we know of in the universe (gamma-ray bursts) and shake the very fabric of space-time via ripples called gravitational waves. GW170817, the merger of two neutron stars witnessed through both its gravitational wave siren and its glow at all wavelengths of light, represents the first multi-messenger detection of one such extreme cosmic bang. Starting from the example of GW170817, in this talk I will discuss how radio light in particular, and gravitational waves, can be used in tandem to unveil the physics of relativistic transients. I will also highlight opportunities and challenges that lie in front of us, as improvements in detectors’ sensitivities will transform a trickle of multi-messenger discoveries into a flood.