Tololo-1247-232

Tololo_1247-232

An image from the HST WFC (using the UVIS channel) taken in 2013 as part of Program 13027.
Observation data (J2000 epoch)
Right ascension 12h 50m 18:80s
Declination −23° 33′ 57:0″
Redshift 0.0480
Distance 652,000,000
Type Starburst galaxy
Apparent magnitude (V) -21
Notable features Lyman Continuum leaker
Other designations
Tol 1247, EC 12476-2317, To 1247

Tololo-1247-232 (Tol 1247 or T1247)) is a small galaxy at a distance of 652,000,000 light-years (200,000,000 parsecs) (redshift z=0.0480).[1] It is situated in the southern equatorial constellation of Hydra. Visually Tol 1247 appears to be an irregular or possibly a barred spiral galaxy.[2] Tol 1247 is named after the surveys that were carried at the Cerro Tololo Inter-American Observatory (CTIO), the first of which was in 1976.[3] It is one of only four galaxies in the local universe known to emit Lyman Continuum photons (LyC).[4]

Background

The Victor M. Blanco Telescope at CTIO

Tol 1247-232 first appeared in the literature in 1985.[5] These observations were carried out using the IR photometer at the CTIO 4m telescope (renamed the Victor Blanco telescope). The aim of the study was to take Near Infrared broad band photometry of Violent Star Formation Regions.[5] The NASA/IPAC Extragalactic Database (NED) gives 28 citations for the original Melnick et al. 1985 paper.[6]

Six years later it was identified as an HII galaxy in the paper 'A spectrophotometric catalogue of HII galaxies', a study of 425 emission-line galaxies.[7] Tol 1247 has also been classified as a Starburst galaxy, a Blue Compact Dwarf and a Wolf-Rayet galaxy.[2]

Lyman Continuum Leakage

Tol 1247 is one of four galaxies in the local universe that have been identified as leaking Lyman Continuum photons; the others being Haro 11, GP J0925 and J0921+4509.[1][4][8] It should be noted that in 2014, at least 2 other galaxies were put forward as possible LyC 'leakers'. These are: GP1219+15 and Tololo-1214-277.[9][10] Tol 1214 was first observed in the original 1976 Tololo survey.[3]

LyC leakage is crucial to the process known as Reionization which is theorised to have occurred between redshift z=11 and z=7, that is to say within the first 10% of the age of the Universe.[11] In general terms, the cosmic reionization is, after recombination, the second major phase-change of hydrogen in the universe.[2] The reionization, sometimes known as the 'Epoch of Reionization', starts when the first ionizing sources appear and begin producing photons capable of ionizing the surrounding medium, and ends when all of the intergalactic medium (IGM) is ionized.[2] LyC photons are theorised to be the particles responsible for this process.

The first published detection of Lyman Continuum photons from Tol 1247 was made in 2013 by Leitet et al. using data from the Far Ultraviolet Spectroscopic Explorer (FUSE).[1] The abstract states that: "We apply a new background subtraction routine on archival data from FUSE, in order to study local galaxies in search for possible Lyman Continuum (LyC) leakage. In the process, for the first time a stacked spectrum in the LyC is produced for local galaxies."[1] The abstract also states: "Out of the eight galaxies [studied], only one was found to have significant LyC leakage, Tol 1247-232 (S/N=5.2). This is the second detection of a leaking galaxy in the local universe."[1] Their results indicate a LyC leakage of approximately 2.5% (2.4% with possible variations of +0.9 or -0.8%).

In a as yet unpublished follow-up study by Christoffer Fremling of Stockholm University for his MSc thesis in 2013, data was used from the ESO New Technology Telescope and the Nordic Optical Telescope to obtain measurements. The results give a LyC leakage of approximately 5% (4.9% with possible variations of +1.2 or -1.1%).[2]

The AlbaNova main building.

In August 2014, a 3-day workshop was held at the AlbaNova University Center, part of Stockholm University, titled: "Lyman Continuum Leakage and Cosmic Reionization".[12] This workshop focused on: "Current and future efforts to constrain the LyC escape fraction of galaxies at both low and high redshift, and the impact that this is likely to have on our understanding of cosmic reionization."[12] Among the lecture abstracts is one titled: "The escape of ionizing radidation from local starburst galaxies: revised Lyman continuum escape fractions for Tololo 1247-232 and Haro 11." by C.U. Fremling (U Stockholm), E. Zackrisson, (U Stockholm), A. Inoue, (Osaka Sangyo U).[12] The abstract states: "We find that our Hα and IR-based escape fraction estimates are quite different from previous results. For Tol 1247-232 we find that only a small fraction of the intrinsic Lyman continuum photons are absorbed by dust, resulting in an escape fraction of ~9%, substantially higher than the previous estimate by Leitet et al. (2013)."[12]

Direct Detection of LyC Escape from Local Starburst Galaxies with the COS

A study was accepted by the Astrophysical Journal in March 2016 which reported detection of LyC emission from 3 galaxies, one of which was Tol 1247.[13] The study was the result of HST program 13325 which occurred between December 2013 and May 2014.[14] The three galaxies studied were Tol 1247, Tol 0440-381 and Mrk 54 using the Cosmic Origins Spectrograph (COS).

Quoting from the study's abstract: "We report on the detection of Lyman continuum radiation in two nearby starburst galaxies. Tol 0440-381, Tol 1247-232 and Mrk 54 were observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescopes."[13] Further on: "We detect Lyman continuum in all three galaxies. However, we conservatively interpret the emission in Tol 0440-381 as an upper limit due to possible contamination by geocoronal Lyman series lines. We determined the current star-formation properties from the far-ultraviolet continuum and spectral lines and used synthesis models to predict the Lyman continuum radiation emitted by the current population of hot stars. We discuss the various model uncertainties such as, among others, atmospheres and evolution models. Lyman continuum escape fractions were derived from a comparison between the observed and predicted Lyman continuum fluxes. Tol 1247-232, Mrk 54 and Tol 0440-381 have absolute escape fractions of (4.5 ± 1.2)%, (2.5 ± 0.72)% and <(7.1 ± 1.1)%, respectively."[13] This study confirms the escape of LyC from T1247.

Further Studies

An image from the HST WFC of Tol 1247, which was observed in 2013 as part of program 13027. This is a combination (by stacking) of several images made by William Keel (University of Alabama) in 2015.

Observing Program 13027 by the Hubble Space Telescope (HST) took place in June 2013.[15] The abstract for Program 13027 states that Tol 1247: "Is a unique galaxy in the local universe in that it is the best Lyman continuum emitter candidate in the whole FUSE archive." It continues: "This galaxy has an enormous potential as an astrophysical laboratory where the fate and transport of ionizing and hydrogen recombination line photons can be studied in detail."[15]

Observing Program 13702 by the HST was scheduled for January 2015.[16] The abstract for Program 13702 states: "We propose to map the optically thin regions in the only two, known Lyman-continuum (LyC) emitting galaxies in the local universe, Haro 11 and Tol 1247-232." It continues: "Together with existing data, our results will clarify the conditions for LyC emission and will yield more realistic estimates of the escape fraction of LyC radiation from these galaxies."[16]

In September 2014, Tol 1247 was observed by the NRAO Very Large Array as in proposal VLA/14B-194.[17][18] The observation took approximately 3 hours by 27 antennae using the L-band receiver (1–2 GHz), so as to look for a 21 cm signal for neutral Hydrogen (H1) at 1420.4 MHz.[18] The proposal 14B-194 states: "This single target is of enormous interest to scientific communities studying both local starburst astrophysics, and high-z galaxies and reionization, as one of the very few nearby objects that shows significant emission of ionizing Lyman continuum radiation."[17]

See also

References

  1. 1 2 3 4 5 E. Leitet; N. Bergvall; M. Hayes; S. Linné; et al. (2013). "Escape of Lyman continuum radiation from local galaxies. Detection of leakage from the young starburst Tol 1247-232". Astronomy & Astrophysics 553. arXiv:1302.6971v2. Bibcode:2013A&A...553A.106L. doi:10.1051/0004-6361/201118370.
  2. 1 2 3 4 5 U. Christoffer Fremling (6 June 2013). "Leakage of ionizing radiation from the nearby galaxy Tololo 1247-232" (PDF). The University of Stockholm. pp. 1–117. Retrieved 4 February 2015.
  3. 1 2 M.G. Smith; C. Aguirre; M. Zemelman (1976). "Emission-line galaxies and quasars. II - The classification systems and list N1, declination not exceeding about -27.5 deg, galactic latitude not less than about +20 deg". Astrophysical Journal Supplement Series 32: 217–231. Bibcode:1976ApJS...32..217S. doi:10.1086/190397.
  4. 1 2 Dawn Erb (2016). "Cosmology: Photons from dwarf galaxy zap hydrogen". Nature (529): 159-160. Bibcode:2016Natur.529..159E. doi:10.1038/529159a.
  5. 1 2 J. Melnick; R. Terlevich; M. Moles (1985). "Near Infrared Photometry of Violent Star Formation Regions". Revista Mexicana de Astronomia y Astrofisica 11: 91. Bibcode:1985RMxAA..11...91M.
  6. ↑ "Reference(s) for object TOLOLO 1247-232". Retrieved February 2015.
  7. ↑ R. Terlevich; J. Melnick; J. Masegosa; M. Moles; et al. (1991). "A spectrophotometric catalogue of HII galaxies". Astronomy and Astrophysics Supplement Series 91 (2). Bibcode:1991A&AS...91..285T.
  8. ↑ S. Borthakur; T.M. Heckman; C. Leitherer; R.A. Overzier (2014). "A Local Clue to the Reionization of the Universe". Science. arXiv:1410.3511v1. Bibcode:2014Sci...346..216B. doi:10.1126/science.1254214.
  9. ↑ A. E. Jaskot & M. S. Oey (2014). "Linking Ly-alpha and Low-Ionization Transitions at Low Optical Depth". The Astrophysical Journal Letters 791 (2). arXiv:1406.4413v2. Bibcode:2014ApJ...791L..19J. doi:10.1088/2041-8205/791/2/L19.
  10. ↑ A. Verhamme; I. Orlitova; D. Schaerer; M. Hayes (2014). "On the use of Lyman-alpha to detect Lyman continuum leaking galaxies". arXiv:1404.2958v1 [astro-ph.GA].
  11. ↑ D.N. Spergel; et al. (2006). "Three-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Implications for Cosmology". The Astrophysical Journal Supplement Series 170 (2): 377–408. arXiv:astro-ph/0603449v2. Bibcode:2007ApJS..170..377S. doi:10.1086/513700.
  12. 1 2 3 4 "Lyman Continuum Leakage and Cosmic Reionization Workshop" (PDF). The University of Stockholm. August 2014. Retrieved February 2015.
  13. 1 2 3 C. Leitherer; S. Hernandez; J.C. Lee; M. S. Oey (21 March 2016). "Direct Detection of Lyman Continuum Escape from Local Starburst Galaxies with the Cosmic Origins Spectrograph". arXiv:1603.06779v1. Bibcode:2016arXiv160306779L.
  14. ↑ C. Leitherer. "Pushing COS to the {Lyman-}Limit". Barbara A. Mikulski Archive for Space Telescopes. Retrieved 19 April 2016.
  15. 1 2 G. Oestlin; N. Bergvall; M. Hayes; E. Zackrisson; et al. (June 2013). "Escape of Lyman photons from Tololo 1247-232". STSCI. Retrieved 4 February 2015.
  16. 1 2 S. Oey; J. Lopez-Hernandez; B. James; A. Jaskot (January 2015). "Mapping the LyC-Emitting Regions of Local Galaxies". Space Telescope Science Institute. Retrieved February 2015.
  17. 1 2 M. Hayes; et al. (February 2014). "Where is the HI in the Strongest Low Redshift Lyman Continuum Emitting Galaxy?". NRAO. Retrieved 18 March 2015.
  18. 1 2 "VLA Observing Log" (PDF). NRAO. 20 September 2014. Retrieved 18 March 2015.

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