skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Catching Tidal Dwarf Galaxies at a Later Evolutionary Stage with ALFALFA
Abstract We present deep optical imaging and photometry of four objects classified as “Almost-Dark” galaxies in the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey because of their gas-rich nature and extremely faint or missing optical emission in existing catalogs. They have H i masses of 10 7 –10 9 M ⊙ and distances of ∼9–100 Mpc. Observations with the WIYN 3.5 m telescope and One Degree Imager reveal faint stellar components with central surface brightnesses of ∼24–25 mag arcsec − 2 in the g band. We also present the results of H i synthesis observations with the Westerbork Synthesis Radio Telescope. These Almost-Dark galaxies have been identified as possible tidal dwarf galaxies (TDGs) based on their proximity to one or more massive galaxies. We demonstrate that AGC 229398 and AGC 333576 likely have the low dark matter content and large effective radii representative of TDGs. They are located much farther from their progenitors than previously studied TDGs, suggesting they are older and more evolved. AGC 219369 is likely dark matter dominated, while AGC 123216 has a dark matter content that is unusually high for a TDG, but low for a normal dwarf galaxy. We consider possible mechanisms for the formation of the TDG candidates such as a traditional major merger scenario and gas ejection from a high-velocity flyby. Blind H i surveys like ALFALFA enable the detection of gas-rich, optically faint TDGs that can be overlooked in other surveys, thereby providing a more complete census of the low-mass galaxy population and an opportunity to study TDGs at a more advanced stage of their life cycle.  more » « less
Award ID(s):
2045369 2045371 2009894
PAR ID:
10434570
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
The Astronomical Journal
Volume:
165
Issue:
5
ISSN:
0004-6256
Page Range / eLocation ID:
197
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, The Astronomical Journal)
    Abstract We present results from deep H i and optical imaging of AGC 229101, an unusual H i source detected at v helio =7116 km s −1 in the Arecibo Legacy Fast ALFA (ALFALFA) blind H i survey. Initially classified as a candidate “dark” source because it lacks a clear optical counterpart in Sloan Digital Sky Survey (SDSS) or Digitized Sky Survey 2 (DSS2) imaging, AGC 229101 has 10 9.31±0.05 M ⊙ of H i , but an H i line width of only 43 ± 9 km s −1 . Low-resolution Westerbork Synthesis Radio Telescope (WSRT) imaging and higher-resolution Very Large Array (VLA) B-array imaging show that the source is significantly elongated, stretching over a projected length of ∼80 kpc. The H i imaging resolves the source into two parts of roughly equal mass. WIYN partially populated One Degree Imager (pODI) optical imaging reveals a faint, blue optical counterpart coincident with the northern portion of the H i . The peak surface brightness of the optical source is only μ g ∼ 26.6 mag arcsec −2 , well below the typical cutoff that defines the isophotal edge of a galaxy, and its estimated stellar mass is only 10 7.32±0.33 M ⊙ , yielding an overall neutral gas-to-stellar mass ratio of M / M * = 98 − 52 + 111 . We demonstrate the extreme nature of this object by comparing its properties with those of other H i -rich sources in ALFALFA and the literature. We also explore potential scenarios that might explain the existence of AGC 229101, including a tidal encounter with neighboring objects and a merger of two dark H i clouds. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal Letters)
    Abstract The two sources AGC 226178 and NGVS 3543, an extremely faint, clumpy, blue stellar system and a low surface brightness dwarf spheroidal, are adjacent systems in the direction of the Virgo cluster. Both have been studied in detail previously, with it being suggested that they are unrelated normal dwarf galaxies or that NGVS 3543 recently lost its gas through ram pressure stripping and AGC 226178 formed from this stripped gas. However, with Hubble Space Telescope Advanced Camera for Surveys imaging, we demonstrate that the stellar population of NGVS 3543 is inconsistent with being at the distance of the Virgo cluster and that it is likely a foreground object at approximately 10 Mpc, whereas the stellar population of AGC 226178 is consistent with it being a very young (10–100 Myr) object in the Virgo cluster. Through a reanalysis of the original ALFALFA H i detection, we show that AGC 226178 likely formed from gas stripped from the nearby dwarf galaxy VCC 2034, a hypothesis strengthened by the high metallicity measured with MUSE VLT observations. However, it is unclear whether ram pressure or a tidal interaction is responsible for stripping the gas. Object AGC 226178 is one of at least five similar objects now known toward Virgo. These objects are all young and unlikely to remain visible for over ∼500 Myr, suggesting that they are continually produced in the cluster. 
    more » « less
  3. ; ; ; ; ; (, The Astrophysical Journal)
    Abstract OH megamasers (OHMs) are extragalactic masers found primarily in gas-rich galaxy major mergers. To date, only ∼120 OHMs have been cataloged since their discovery in 1982, and efforts to identify distinct characteristics of OHM host galaxies have remained inconclusive. As radio astronomy advances with next-generation telescopes and extensive 21 cm Hisurveys, precursors to the Square Kilometre Array are expected to detect the 18 cm OH masing line with significantly increased frequency, potentially expanding the known OHM population tenfold. These detections, however, risk confusion with lower-redshift Hiemitters unless accompanied by independent spectroscopic redshifts. Building on methods proposed by Roberts et al. for distinguishing these interloping OHMs via near- to mid-IR photometry and emission line frequencies, we apply these techniques to data from the Arecibo Legacy Fast ALFA [AreciboL-band Feed Array] (ALFALFA) survey and a preliminary Aperture Tile In Focus (Apertif) Hiemission line catalog from the Westerbork Synthesis Radio Telescope. Our study, utilizing the Apache Point Observatory 3.5 m telescope to obtain optical spectroscopic redshifts of 142 candidates (107 from ALFALFA and 35 from Apertif), confirms five new OHM host galaxies and reidentifies two previously catalogued OHMs misclassified as Hiemitters in ALFALFA. These findings support the predictions from Roberts et al. and underscore the evolving landscape of radio astronomy in the context of next-generation telescopes. 
    more » « less
  4. ; ; ; ; ; ; ; (, The Astronomical Journal)
    Abstract We present results from an optical search for Local Group dwarf galaxy candidates associated with the Ultra-Compact High Velocity Clouds (UCHVCs) discovered by the ALFALFA neutral hydrogen survey. The ALFALFA UCHVCs are isolated, compact Hiclouds with projected sizes, velocities, and estimated Himasses that suggest they may be nearby dwarf galaxies, but that have no clear counterpart in existing optical survey data. We observed 26 UCHVCs with the WIYN 3.5 m telescope and One Degree Imager (ODI) in two broadband filters and searched the images for resolved stars with properties that match those of stars in typical dwarf galaxies at distances <2.5 Mpc. We identify one promising dwarf galaxy candidate at a distance of ∼570 kpc associated with the UCHVC AGC 268071, and five other candidates that may deserve additional follow-up. We carry out a detailed analysis of ODI imaging of a UCHVC that is close in both projected distance and radial velocity to the outer-halo Milky Way globular cluster Pal 3. We also use our improved detection methods to reanalyze images of five UCHVCs that were found to have possible optical counterparts during the first phase of the project, and confirm the detection of a possible stellar counterpart to the UCHVC AGC 249525 at an estimated distance of ∼2 Mpc. We compare the optical and Hiproperties of the dwarf galaxy candidates to the results from recent theoretical simulations that model satellite galaxy populations in group environments, as well as to the observed properties of galaxies in and around the Local Group. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, American Astronomical Society ... meeting)
    We present VLA HI imaging of the "Almost Dark" galaxies AGC 227982, AGC 268363, and AGC 219533. Selected from the ALFALFA survey, "Almost Dark" galaxies have significant HI reservoirs but lack an obvious stellar counterpart in survey-depth ground-based optical imaging. These three HI-rich objects harbor some of the most extreme levels of suppressed star formation amongst the isolated sources in the ALFALFA catalog. Our new multi-configuration, high angular (~20") and spectral (1.7 km/s) resolution HI observations produce spatially resolved column density and velocity distribution moment maps. We compare these images to Sloan Digitized Sky Survey (SDSS) optical images. By localizing the HI gas, we identify previously unknown optical components (offset from the ALFALFA pointing center) for AGC 227982 and AGC 268363, and confirm the association with a very low surface brightness stellar counterpart for AGC 219533. Baryonic masses are derived from VLA flux integral values and ALFALFA distance estimates, giving answers consistent with those derived from ALFALFA fluxes. All three sources appear to have fairly regular HI morphologies and show evidence of ordered rotation.Support for this work was provided by NSF grant 1211683 to JMC at Macalester College. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email