Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

Infrared properties of close pairs of galaxies

Abstract: We discuss spectroscopy and IR photometry for a complete sample of ~800 galaxies in close pairs objectively selected from the second Center for Astrophysics redshift survey. We use the Two Micron All Sky Survey to compare near-IR color-color diagrams for our sample with the Nearby Field Galaxy Sample and with a set of IRAS flux-limited pairs from Surace and coworkers. We construct a basic statistical model to explore the physical sources of the substantial differences among these samples. The model explains the spread of near-IR colors and is consistent with a picture in which central star formation is triggered by the galaxy-galaxy interaction before a merger occurs. For 160 galaxies we report new, deep JHK photometry within our spectroscopic aperture, and we use the combined spectroscopic and photometric data to explore the physical conditions in the central bursts. We find a set of objects with H - K ≥ 0.45 and with a large F_(FIR)/F_H. We interpret the very red H - K colors as evidence for 600-1000 K dust within compact star-forming regions, perhaps similar to super star clusters identified in individual well-studied interacting galaxies. The galaxies in our sample are candidate "hidden" bursts or, possibly, "hidden" active galactic nuclei. Over the entire pair sample, both spectroscopic and photometric data show that the specific star formation rate decreases with the projected separation of the pair. The data suggest that the near-IR color-color diagram is also a function of the projected separation; all of the objects with central near-IR colors indicative of bursts of star formation lie at small projected separation.

X-ray Scaling Relation in Early-Type Galaxies: Dark Matter as a Primary Factor in Retaining Hot Gas

Abstract: We have revisited the X-ray scaling relations of early type galaxies (ETG) by investigating, for the first time, the LX,Gas - MTotal relation in a sample of 14 ETGs. In contrast to the large scatter (by a factor of 102-103) in the LX,Total - LB relation, we found a tight correlation between these physically motivated quantities with a rms deviation of a factor of 3 in LX,Gas = 1038 - 1043 erg s-1 or MTotal = a few x 1010 - a few x 1012 Mo. More striking, this relation becomes even tighter with a rms deviation of a factor of 1.3 among the gas-rich galaxies (with LX,Gas > 1040 erg s-1). In a simple power-law form, the new relation is (LX,Gas / 1040 erg s-1) = (MTotal / 3.2 x 1011 Mo)3. This relation is also consistent with the steep relation between the gas luminosity and temperature, LX,Gas ~ TGas4.5, identified by Boroson, Kim & Fabbiano (2011), if the gas is virialized. Our results indicate that the total mass of an ETG is the primary factor in regulating the amount of hot gas. Among the gas-poor galaxies (with LX,Gas < a few x 1039 erg s-1), the scatter in the LX,Gas - MTotal (and LX,Gas - TGas) relation increases, suggesting that secondary factors (e.g., rotation, flattening, star formation history, cold gas etc.) may become important.

Properties of a coronal shock wave as a driver of early sep acceleration

Abstract: Coronal mass ejectmons (CMEs) are thought to drive collisionless shocks in the solar corona, which in turn have been shown to be capable of accelerating solar energetic particles (SEPs) in minutes. It has been notoriously difficult to extract information about energetic particle spectra in the corona, owing to a lack of in situ measurements. It is possible, however, to combine remote observations with data-driven models in order to deduce coronal shock properties relevant to the local acceleration of SEPs and their heliospheric connectivity to near-Earth space. We present such novel analysis applied to the 2011 May 11 CME event on the western solar limb, focusing on the evolution of the eruption-driven, dome-like shock wave observed by the Atmospheric Imaging Assembly (AIA) EUV telescopes on board the Solar Dynamics Observatory spacecraft. We analyze the shock evolution and estimate its strength using emission measure modeling. We apply a new method combining a geometric model of the shock front with a potential field source surface model to estimate time-dependent field-to-shock angles and heliospheric connectivity during shock passage in the low corona. We find that the shock was weak, with an initial speed of ~450 km s–1. It was initially mostly quasi-parallel, but a significant portion of it turned quasi-perpendicular later in the event. There was good magnetic connectivity to near-Earth space toward the end of the event as observed by the AIA instrument. The methods used in this analysis hold a significant potential for early characterization of coronal shock waves and forecasting of SEP spectra based on remote observations.

Differential Flow Speeds of Ions of the Same Element: Effects on Solar Wind Ionization Fractions

Abstract: In previous studies of solar wind ion fractions it has always been assumed that ions of the same element flow with the same flow speed. In the present paper, we investigate the effects of differential flow speeds between different ionization states of the same element on the formation of O, C, Mg, Si, and Fe ions. We show that if the difference in flow speeds of adjacent ions, vi and vi+1, is large, the discrepancy between observed in situ ion fractions and low coronal electron temperature can be significantly reduced. The calculations are carried out for a radial profile of the electron temperature chosen in agreement with Solar Ultraviolet Measurement of Emitted Radiation (SUMER) measurements of coronal dark lanes and with two radial profiles of the electron density representing lower and upper observational limits. In order for the differential flow speeds to close the gap between the ion fractions observed in situ and the ones predicted from the low electron temperature observed in the corona, the differential flow speeds have to be extremely large in the regions where the ions are formed, e.g., below 1.5RS for O ions and below 2.5RS for Si ions; and in the case of Si, the coronal electron density has to be at the upper limit of observed values. In the cases of C, O, Mg, and Fe, the lower limit on the electron density is also acceptable.

CH Cygni. I. Observational Evidence for a Disk-Jet Connection

Abstract: We investigate the role of accretion in the production of jets in the symbiotic star CH Cygni. Assuming that the rapid stochastic optical variations in CH Cygni come from the accretion disk, as in cataclysmic variables, we use changes in this flickering to diagnose the state of the disk in 1997. At that time, CH Cygni dropped to a very low optical state, and Karovska et al. report that a radio jet was produced. For approximately 1 yr after the jet production, the amplitude of the fastest (timescale of minutes) variations was significantly reduced, although smooth, hour-timescale variations were still present. This light-curve evolution indicates that the inner disk may have been disrupted, or emission from this region suppressed, in association with the mass ejection event. We describe optical spectra that support this interpretation of the flickering changes. The simultaneous state change, jet ejection, and disk disruption suggest a comparison between CH Cygni and some black hole candidate X-ray binaries that show changes in the inner-disk radius in conjunction with discrete ejection events on a wide range of timescales (e.g., the microquasar GRS 1915+105 and XTE J1550� 564). Subject headings: accretion, accretion disks — binaries: symbiotic — instabilities — stars: winds, outflows — techniques: photometric