Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInfrared Properties of Close Pairs of Galaxies
603
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We discuss spectroscopy and infrared photometry for a complete sample of ~ 800 galaxies in close pairs objectively selected from the CfA2 redshift survey. We use 2MASS to compare near infrared color-color diagrams for our sample with the Nearby Field Galaxy Sample and with a set of IRAS flux-limited pairs from Surace et al. 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 infrared colors and is consistent with a picture where 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 AGN. 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 infrared color-color diagram is also a function of the projected separation; all of the objects with central near infrared colors indicative of bursts of star formation lie at small projected separation.
rate research
Read More
We analyze new optical spectra of a sample of 502 galaxies in close pairs and n-tuples, separated by <= 50/h kpc. We extracted the sample objectively from the CfA2 redshift survey, without regard to the surroundings of the tight systems. We probe the relationship between star formation and the dynamics of the systems of galaxies. The equivalent widths of Halpha (EW(Halpha) and other emission lines anti-correlate strongly with pair spatial separation (Delta D) and velocity separation. We use the measured EW(Halpha) and the starburst models of Leitherer et al. to estimate the time since the most recent burst of star for- mation began for each galaxy. In the absence of a large contribution from an old stellar population to the continuum around Halpha, the observed Delta D -- EW(Halpha) correlation signifies that starbursts with larger separations on the sky are, on average, older. By matching the dynamical timescale to the burst timescale, we show that the data support a simple picture in which a close pass initiates a starburst; EW(Halpha) decreases with time as the pair separation increases, accounting for the anti-correlation. This picture leads to a method for measuring the duration and the initial mass function of interaction-induced starbursts: our data are compatible with the starburst and orbit models in many respects, as long as the starburst lasts longer than sim10^8 years and the delay between the close pass and the initiation of the starburst is less than a few times 10^7 years. If there is no large contribution from an old stellar population to the continuum around Halpha the Miller-Scalo and cutoff (M <= 30 M_sun) Salpeter initial mass functions fit the data much better than a standard Salpeter IMF. (Abridged.)
We extract from the Sloan Digital Sky Survey a sample of 347 systems involving early type galaxies separated by less than 30 kpc, in projection, and 500 km/s in radial velocity. These close pairs are likely progenitors of dry mergers. The (optical) spectra is used to determine how the interaction affects the star formation history and nuclear activity of the galaxies. The emission lines (or lack thereof) are used to classify the sample into AGN, star forming or quiescent. Increased AGN activity and reduced star formation in early-type pairs that already appear to be interacting indicate that the merging process changes the nature of nebular activity, a finding that is also supported by an increase in AGN luminosity with decreasing pair separation. Recent star formation is studied on the absorption line spectra, both through principal component analysis as well as via a comparison of the spectra with composite stellar population models. We find that the level of recent star formation in close pairs is raised relative to a control sample of early-type galaxies. This excess of residual star formation is found throughout the sample of close pairs and does not correlate with pair separation or with visual signs of interaction. Our findings are consistent with a scenario whereby the first stage of the encounter (involving the outer parts of the halos) trigger residual star formation, followed by a more efficient inflow towards the centre -- switching to an AGN phase -- after which the systems are quiescent.
(Abriged) Our goal here is to provide merger frequencies that encompass both major and minor mergers, derived from close pair statistics. We use B-band luminosity- and mass-limited samples from an Spitzer/IRAC-selected catalogue of GOODS-S. We present a new methodology for computing the number of close companions, Nc, when spectroscopic redshift information is partial. We select as close companions those galaxies separated by 6h^-1 kpc < rp < 21h^-1 kpc in the sky plane and with a difference Delta_v <= 500 km s^-1 in redshift space. We provide Nc for four different B-band-selected samples. Nc increases with luminosity, and its evolution with redshift is faster in more luminous samples. We provide Nc of M_star >= 10^10 M_Sun galaxies, finding that the number including minor companions (mass ratio >= 1/10) is roughly two times the number of major companions alone (mass ratio >= 1/3) in the range 0.2 <= z < 1.1. We compare the major merger rate derived by close pairs with the one computed by morphological criteria, finding that both approaches provide similar merger rates for field galaxies when the progenitor bias is taken into account. Finally, we estimate that the total (major+minor) merger rate is ~1.7 times the major merger rate. Only 30% to 50% of the M_star >= 10^10 M_Sun early-type (E/S0/Sa) galaxies that appear z=1 and z=0 may have undergone a major or a minor merger. Half of the red sequence growth since z=1 is therefore unrelated to mergers.
The unprecedented sensitivity of the Spitzer Space Telescope has enabled us for the first time to detect a large sample of Blue Compact Dwarf galaxies (BCDs), which are intrinsically faint in the infrared. In the present paper we present a summary of our findings which providing essential information on the presence/absence of the Polycyclic Aromatic Hydrocarbon features in metal-poor environments. In addition, using Spitzer/IRS high-resolution spectroscopy, we study the elemental abundances of neon and sulfur in BCDs and compare with the results from optical studies. Finally, we present an analysis of the mid- and far-infrared to radio correlation in low luminosity low metallicity galaxies.
We present spectra of the nuclear regions of 50 nearby (D = 1 - 92 Mpc, median = 20 Mpc) galaxies of morphological types E to Sm. The spectra, obtained with the Gemini Near-IR Spectrograph on the Gemini North telescope, cover a wavelength range of approximately 0.85-2.5 microns at R~1300--1800. There is evidence that most of the galaxies host an active galactic nucleus (AGN), but the range of AGN luminosities (log (L2-10 keV [erg/s]) = 37.0-43.2) in the sample means that the spectra display a wide variety of features. Some nuclei, especially the Seyferts, exhibit a rich emission-line spectrum. Other objects, in particular the type 2 Low Ionisation Nuclear Emission Region galaxies, show just a few, weak emission lines, allowing a detailed view of the underlying stellar population. These spectra display numerous absorption features sensitive to the stellar initial mass function, as well as molecular bands arising in cool stars, and many other atomic absorption lines. We compare the spectra of subsets of galaxies known to be characterised by intermediate-age and old stellar populations, and find clear differences in their absorption lines and continuum shapes. We also examine the effect of atmospheric water vapor on the signal-to-noise ratio achieved in regions between the conventional NIR atmospheric windows, of potential interest to those planning observations of redshifted emission lines or other features affected by telluric H2O. Further exploitation of this data set is in progress, and the reduced spectra and data reduction tools are made available to the community.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
