Star Formation and the Interstellar Medium in Nearby Tidal Streams (SAINTS)

TL;DR

This study uses infrared observations to analyze star formation and interstellar medium properties in tidal streams of interacting galaxies, revealing diverse star-forming knots with distinct infrared characteristics and dust properties.

Contribution

It provides a detailed infrared analysis of tidal star forming knots across multiple systems, identifying their stellar masses, dust features, and emission properties, which advances understanding of star formation in tidal environments.

Findings

Detected warm H2 in several tidal regions.

Identified two distinct infrared color groups among tidal star forming knots.

Found that stellar mass correlates with 8 um luminosity and varies across systems.

Abstract

We compare Spitzer Infrared Spectrograph observations of SQ-A & SQ-B in Stephan's Quintet, Ambartzumian's knot in Arp 105, Arp 242-N3, Arp 87-N1, a bridge star forming region, NGC 5291 N and NGC 5291 S. The PAHs tend to be mainly neutral grains with a typical size of 50 - 100 carbon atoms. The interstellar radiation field is harder than typical starburst galaxies, being similar to that found in dwarf galaxies. The neon line ratios are consistent with a recent episode of star formation. We detect warm H2 in SQ-A, Arp 87N1 and SQ-B. Using our 8 um images of 14 interacting systems we identify 62 tidal star forming knots (TSFKs). The estimated stellar masses range from super star cluster (10^4-10^6 Msun) to TDG (~10^9 Msun) sizes. The stellar mass, with some scatter, scales with the 8 um luminosity and tends to be an order of magnitude smaller than the KISS sample of star forming dwarfs. An exception to this are the more massive TSFKs in Arp 242. The TSFKs, form two distinct clumps in a mid-infrared color diagram. There are 38 red-TSFKs with [4.5] - [8.0] > 3 and [3.6] - [4.5] < 0.4. This populations has significantly enhanced non-stellar emission, most likely due to PAHs and/or hot dust. The second group of 21 sources has 1.2 < [4.5] - [8.0] < 3 and [3.6] - [4.5] < 0.4, these colors are similar to star forming dwarf and spiral galaxies. The redder [4.5] - [8.0] population tends to have the sources with a rising 8-24 um SED while the blue population tends to contain the sources with a descending SED. The rising SED is typical of spiral and starburst galaxies with a dominant 40 - 60 K dust component and the declining SED probably indicates a dominant hot dust component.