Browsing by Subject "continuum emission"

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Fragmentation And Evolution Of Molecular Clouds. II. The Effect Of Dust Heating
(2010-02) Urban, Andrea; Martel, Hugo; Evans, Neal J.; Urban, Andrea; Evans, Neal J.
We investigate the effect of heating by luminosity sources in a simulation of clustered star formation. Our heating method involves a simplified continuum radiative transfer method that calculates the dust temperature. The gas temperature is set by the dust temperature. We present the results of four simulations; two simulations assume an isothermal equation of Stateand the two other simulations include dust heating. We investigate two mass regimes, i. e., 84 M(circle dot) and 671 M(circle dot), using these two different energetics algorithms. The mass functions for the isothermal simulations and simulations that include dust heating are drastically different. In the isothermal simulation, we do not form any objects with masses above 1 M(circle dot). However, the simulation with dust heating, while missing some of the low-mass objects, forms high-mass objects (similar to 20 M(circle dot)) which have a distribution similar to the Salpeter initial mass function. The envelope density profiles around the stars formed in our simulation match observed values around isolated, low-mass star-forming cores. We find the accretion rates to be highly variable and, on average, increasing with final stellar mass. By including radiative feedback from stars in a cluster-scale simulation, we have determined that it is a very important effect which drastically affects the mass function and yields important insights into the formation of massive stars.
Fragmentation And Evolution Of Molecular Clouds. III. The Effect Of Dust And Gas Energetics
(2012-09) Martel, Hugo; Urban, Andrea; Evans, Neal J.; Martel, Hugo; Evans, Neal J.
Dust and gas energetics are incorporated into a cluster-scale simulation of star formation in order to study the effect of heating and cooling on the star formation process. We build on our previous work by calculating separately the dust and gas temperatures. The dust temperature is set by radiative equilibrium between heating by embedded stars and radiation from dust. The gas temperature is determined using an energy-rate balance algorithm which includes molecular cooling, dust-gas collisional energy transfer, and cosmic-ray ionization. The fragmentation proceeds roughly similarly to simulations in which the gas temperature is set to the dust temperature, but there are differences. The structure of regions around sink particles has properties similar to those of Class 0 objects, but the infall speeds and mass accretion rates are, on average, higher than those seen for regions forming only low-mass stars. The gas and dust temperature have complex distributions not well modeled by approximations that ignore the detailed thermal physics. There is no simple relationship between density and kinetic temperature. In particular, high-density regions have a large range of temperatures, determined by their location relative to heating sources. The total luminosity underestimates the star formation rate at these early stages, before ionizing sources are included, by an order of magnitude. As predicted in our previous work, a larger number of intermediate-mass objects form when improved thermal physics is included, but the resulting initial mass function (IMF) still has too few low-mass stars. However, if we consider recent evidence on core-to-star efficiencies, the match to the IMF is improved.
The Lick AGN Monitoring Project 2011: Reverberation Mapping of Markarian 50
(2011-12) Barth, Aaron J.; Pancoast, Anna; Thorman, Shawn J.; Bennert, Vardha N.; Sand, David J.; Li, Weidong; Canalizo, Gabriela; Filippenko, Alexei V.; Gates, Elinor L.; Greene, Jenny E.; Malkan, Matthew A.; Stern, Daniel; Treu, Tommaso; Woo, Jong-Hak; Assef, Roberto J.; Bae, Hyun-Jin; Brewer, Brendon J.; Buehler, Tabitha; Cenko, S. Bradley; Clubb, Kelsey I.; Cooper, Michael C.; Diamond-Stanic, Aleksandar M.; Hiner, Kyle D.; Hoenig, Sebastian F.; Joner, Michael D.; Kandrashoff, Michael T.; Laney, C. David; Lazarova, Mariana S.; Nierenberg, A. M.; Park, Dawoo; Silverman, Jeffrey M.; Son, Donghoon; Sonnenfeld, Alessandro; Tollerud, Erik J.; Walsh, Jonelle L.; Walters, Richard; da Silva, Robert L.; Fumagalli, Michele; Gregg, Michael D.; Harris, Chelsea E.; Hsiao, Eric Y.; Lee, Jeffrey; Lopez, Liliana; Rex, Jacob; Suzuki, Nao; Trump, Jonathan R.; Tytler, David; Worseck, Gabor; Yesuf, Hassen M.; Walsh, Jonelle L.
The Lick AGN Monitoring Project 2011 observing campaign was carried out over the course of 11 weeks in spring 2011. Here we present the first results from this program, a measurement of the broad-line reverberation lag in the Seyfert 1 galaxy Mrk 50. Combining our data with supplemental observations obtained prior to the start of the main observing campaign, our data set covers a total duration of 4.5 months. During this time, Mrk 50 was highly variable, exhibiting a maximum variability amplitude of a factor of similar to 4 in the U-band continuum and a factor of similar to 2 in the H beta line. Using standard cross-correlation techniques, we find that H beta and H gamma lag the V-band continuum by tau(cen) = 10.64(-0.93)(+0.82) and 8.43(-1.28)(+1.30) days, respectively, while the lag of He II lambda 4686 is unresolved. The H beta line exhibits a symmetric velocity-resolved reverberation signature with shorter lags in the high-velocity wings than in the line core, consistent with an origin in a broad-line region (BLR) dominated by orbital motion rather than infall or outflow. Assuming a virial normalization factor of f = 5.25, the virial estimate of the black hole mass is (3.2 +/- 0.5) x 10(7) M-circle dot. These observations demonstrate that Mrk 50 is among the most promising nearby active galaxies for detailed investigations of BLR structure and dynamics.
A Parameter Study Of The Dust And Gas Temperature In A Field Of Young Stars
(2009-06) Urban, Andrea; Evans, Neal J.; Doty, Steven D.; Urban, Andrea; Evans, Neal J.
We model the thermal effect of young stars on their surrounding environment in order to understand clustered star formation. We take radiative heating of dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling into account. Using DUSTY, a spherical continuum radiative transfer code, we model the dust temperature distribution around young stellar objects with various luminosities and surrounding gas and dust density distributions. We have created a grid of dust temperature models, based on our modeling with DUSTY, which we can use to calculate the dust temperature in a field of stars with various parameters. We then determine the gas temperature assuming energy balance. Our models can be used to make large-scale simulations of clustered star formation more realistic.