Author Topic: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies  (Read 24908 times)

zookeeperKevin

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Re: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies
« Reply #75 on: September 10, 2012, 08:32:50 am »
The Peas are characterised as
"deviant 'low-metallicity starbursts'".

:D

They really are.

Rick Nowell

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Re: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies
« Reply #76 on: September 18, 2012, 05:26:20 pm »
New paper on:
"H and UV luminosities and star formation rates in a large sample of luminous compact galaxies"
authors:  S. L. Parnovsky • I. Y. Izotova • Y. I. Izotov.
http://arxiv.org/pdf/1209.3498v1.pdf

"We present the results of a statistical study of the star formation rates (SFR) derived from the
Galaxy Evolution Explorer (GALEX) observations in the ultraviolet continuum and in the H\alpha
emission line for a sample of about 800 luminous compact galaxies (LCGs). Galaxies in this sample
have a compact structure and include one or several regions of active star formation."

Luminous Compacts are Izotov's larger set of galaxies, of which Green Peas are a subset. In a
complex paper, using Cardamone's 251 Peas which are included in Izotov's 803 LCGs, star
formation rates up to 113 solar masses a year are described.

http://en.wikipedia.org/wiki/GALEX
« Last Edit: September 18, 2012, 08:24:01 pm by Rick Nowell »

NGC3314

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Re: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies
« Reply #77 on: January 04, 2013, 04:06:15 am »
Peas continue to gain popularity:

The Origin and Optical Depth of Ionizing Radiation in the "Green Pea" Galaxies

A.E. Jaskot and M.S. Oey

Quote
Although Lyman continuum (LyC) radiation from star-forming galaxies likely drove the reionization of the Universe, observations of star-forming galaxies at low redshift generally indicate low LyC escape fractions. However, the extreme [O III]/[O II] ratios of the z=0.1-0.3 Green Pea galaxies may be due to high escape fractions of ionizing radiation. To analyze the LyC optical depths and ionizing sources of these rare, compact starbursts, we compare nebular photoionization and stellar population models with observed emission lines in the Peas' SDSS spectra. We focus on the six most extreme Green Peas, the galaxies with the highest [O III]/[O II] ratios and the best candidates for escaping ionizing radiation. The Balmer line equivalent widths and He I 3819 emission in the extreme Peas support young ages of 3-5 Myr, and He II 4686 emission in five extreme Peas signals the presence of hard ionizing sources. Ionization by active galactic nuclei or high-mass X-ray binaries is inconsistent with the Peas' line ratios and ages. Although stacked spectra reveal no Wolf-Rayet (WR) features, we tentatively detect WR features in the SDSS spectra of three extreme Peas. Based on the Peas' ages and line ratios, we find that WR stars, chemically homogeneous O stars, or shocks could produce the observed He II emission. If hot stars are responsible, the Peas' optical depths are ambiguous. However, accounting for emission from shocks lowers the inferred optical depth and suggests that the Peas may be optically thin. The Peas' ages likely optimize the escape of Lyman-continuum radiation; they are old enough for supernovae and stellar winds to reshape the interstellar medium, but young enough to possess large numbers of UV-luminous O or WR stars.

Rick Nowell

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Citations for  2009MNRAS.399.1191C   on the SAO/NASA Astrophysics Data System (ADS) reach 50.

http://adsabs.harvard.edu/cgi-bin/nph-ref_query?bibcode=2009MNRAS.399.1191C&refs=CITATIONS&db_key=AST

zutopian

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Re: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies
« Reply #79 on: October 20, 2013, 02:51:18 pm »
In the attachment is an UKIDSS image of a known green pea
Corresponding SDSS image: http://skyserver.sdss3.org/dr9/en/tools/explore/obj.asp?id=1237664092897083648




Rick Nowell

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Re: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies
« Reply #80 on: December 17, 2013, 02:19:22 pm »
Suggested GP-related holiday reading:

Green pea galaxies could help astronomers understand early universe
http://www.astronomy.com/news/2013/04/green-pea-galaxies-could-help-astronomers-understand-early-universe

A recent paper from Yuri Izotov in which GPs are very prominent:
http://arxiv.org/abs/1310.1559
Multi-wavelength study of 14000 star-forming galaxies from the Sloan Digital Sky Survey.

NGC3314

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Re: Discussion: Green Peas: A Class of Compact Extremely Star-Forming Galaxies
« Reply #81 on: February 19, 2014, 02:15:10 pm »
Conference report by Jaskot and Oey, including UV spectra obtained since their earlier paper:

The Origin and Optical Depth of Ionizing Photons in the Green Pea Galaxies

Quote
Our understanding of radiative feedback and star formation in galaxies at high redshift is hindered by the rarity of similar systems at low redshift. However, the recently identified Green Pea (GP) galaxies are similar to high-redshift galaxies in their morphologies and star formation rates and are vital tools for probing the generation and transmission of ionizing photons. The GPs contain massive star clusters that emit copious amounts of high-energy radiation, as indicated by intense [OIII] 5007 emission and HeII 4686 emission. We focus on six GP galaxies with high ratios of [O III] 5007,4959/[O II] 3727 ~10 or more. Such high ratios indicate gas with a high ionization parameter or a low optical depth. The GP line ratios and ages point to chemically homogeneous massive stars, Wolf-Rayet stars, or shock ionization as the most likely sources of the He II emission. Models including shock ionization suggest that the GPs may have low optical depths, consistent with a scenario in which ionizing photons escape along passageways created by recent supernovae. The GPs and similar galaxies can shed new light on cosmic reionization by revealing how ionizing photons propagate from massive star clusters to the intergalactic medium.


NGC3314

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Extreme emission-line galaxies out to z1 in zCOSMOS-20k I. Sample and characterization of global properties, by R. Amorin et a.

Abstract:
Quote
We present a large sample of 183 extreme emission-line galaxies (EELGs) at redshift 0.11 < z < 0.93 selected from the 20k zCOSMOS Bright Survey by their unusually large [OIII]5007 equivalent widths. Based on emission-line diagnostics, 165 purely star-forming EELGs and 18 narrow-line AGN candidates are identified. Using multiwavelength COSMOS photometry, HST-ACS I-band imaging and optical zCOSMOS spectroscopy we characterize their main physical properties. EELGs are small (R_50 ~ 1.3 kpc), low-mass (M*/Msol~10^7-10^10) galaxies forming stars at unusually high rates (SFR~0.1-35 Msol/yr), being among the highest specific SFRs galaxies in zCOSMOS. Consistently, the EELGs are luminous and extremely compact at rest-frame UV wavelengths and include strong Ly-alpha emitters, as revealed by GALEX spectroscopy. Using both direct and strong-line methods, we show that zCOSMOS EELGs are low-metallicity systems (12+log(O/H)=8.16 in the median) including several extremely metal-deficient galaxies (<10% solar). Finally, HST-ACS I-band images reveal that ~80% of the EELGs show non-axisymmetric morphologies, including clumpy and tadpole galaxies, and a significant fraction (~29%) of galaxies with additional low surface brightness features strongly suggesting recent or ongoing interactions. As star-forming dwarfs in the local Universe, EELGs are preferably found in relative isolation. While only very few EELGs belong to compact groups, almost one third of them are found in spectroscopically confirmed loose pairs or triplets. The zCOSMOS EELGs are galaxies caught in a transient and probably early period of their evolution, where they are efficiently building-up a significant fraction of their present-day stellar mass in an ongoing galaxy-wide starburst. Therefore, the EELGs constitute an ideal benchmark for comparison studies between low- and high-redshift low-mass star-forming galaxies.

Forrm the conclusion section:
Quote
In conclusion, we have shown that galaxies selected by their extreme strength of their optical emission lines led us to a homogeneous, representative sample of compact, low-mass, low-metallicity, vigorous star-forming systems identifiable with luminous, higher-z versions of nearby Hii galaxies and Blue Compact Dwarfs. The extreme properties of some of these rare systems closely resemble those of luminous compact galaxies, such as the green peas (Cardamone et al. 2009; Amorın et al. 2010) and other samples of emission line galaxies with very high equivalent widths...

Rick Nowell

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Peas and leaks:
'On the use of Lyman-alpha to detect Lyman continuum leaking galaxies'
A. Verhamme, I. Orlitova, D. Schaerer, M. Hayes
http://arxiv.org/abs/1404.2958

"We propose to infer ionising continuum leaking properties of galaxies by looking at their Lyman-alpha line profiles...
The examination of a sample of 10 local starbursts with high resolution HST-COS Lyman-alpha spectra and known in
the literature as LyC leakers or leaking candidates, corroborates our predictions. Observations of Lyman-alpha profiles
at high resolution should show definite signatures betraying the escape of Lyman continuum photons from star-forming
galaxies."

One GP is "a good candidate for Lyman Continuum leaking":
587735349111947338  a.k.a.  J1219+1526
http://cas.sdss.org/astro/en/tools/explore/obj.asp?id=587735349111947338

Also, this GP is included in Cardamone 2009, Izotov 2011a, Hawley 2012, Jaskot 2013 and Izotov 2013.
 
« Last Edit: April 17, 2014, 08:09:02 am by Rick Nowell »

Rick Nowell

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Peas and ALFALFA:

http://adsabs.harvard.edu/abs/2014AAS...22332803J

Title:   Neutral Gas and Low-Redshift Starbursts: From Infall to Ionization
Authors:   Jaskot, Anne; Oey, M. S.; Salzer, J. J.; Van Sistine, A.; Haynes, M. P.
Publication:   American Astronomical Society, AAS Meeting #223, #328.03

The Arecibo Legacy Fast ALFA Survey
http://egg.astro.cornell.edu/alfalfa/index.php

FROM ABSTRACT:
"To evaluate the impact of radiative feedback in extreme starbursts, we analyze optical spectra of the
Green Pea galaxies, a low-redshift sample selected by their intense [O III] lambda5007 emission and
compact sizes. We use nebular photoionization and stellar population models to constrain the Peas' burst
ages, ionizing sources, and optical depths and find that the Peas are likely optically thin to Lyman continuum
(LyC) radiation. These young starbursts still generate substantial ionizing radiation, while recent supernovae
may have carved holes in the ISM that enhance LyC photon escape into the intergalactic medium. While the
ALFALFA survey demonstrates the role of external processes in triggering starbursts, the Green Peas show
that starbursts' radiation can escape to affect their external environment."

As this was a presentation to the AAS, there is no full paper available.

« Last Edit: May 05, 2014, 01:49:17 pm by Rick Nowell »

NGC3314

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Work connecting Green Peas to processes early in the history of most galaxies continues, now working from new Hubble spectra in the ultraviolet:

Linking Ly-alpha and Low-Ionization Transitions at Low Optical Depth
Authors: A. E. Jaskot and M. S. Oey


Quote
We suggest that low optical depth in the Lyman continuum (LyC) may relate the Ly-alpha emission, C II and Si II absorption, and C II* and Si II* emission seen in high-redshift galaxies. We base this analysis on Hubble Space Telescope COS spectra of four Green Pea (GP) galaxies, which may be analogs of z>2 Ly-alpha emitters (LAEs). In the two GPs with the strongest Ly-alpha emission, the Ly-alpha line profiles do not show the typical effects of resonant scattering. Instead, the Ly-alpha profiles resemble the H-alpha line profiles of evolved star ejecta, suggesting that the Ly-alpha emission originates from a low column density and similar outflow geometry. The weak C II absorption and presence of non-resonant C II* emission in these GPs support this interpretation and imply a low LyC optical depth along the line of sight. In two additional GPs, weak Ly-alpha emission and strong C II absorption suggest a higher optical depth. These two GPs differ in their Ly-alpha profile shapes and C II* emission strengths, however, indicating different inclinations of the outflows to our line of sight. With these four GPs as examples, we explain the observed trends linking Ly-alpha, C II, and C II* in stacked LAE spectra, in the context of optical depth and geometric effects. Specifically, in some galaxies with strong Ly-alpha emission, a low LyC optical depth may allow Ly-alpha to escape with reduced scattering. Furthermore, C II absorption, C II* emission, and Ly-alpha profile shape can reveal the optical depth, constrain the orientation of neutral outflows in LAEs, and identify candidate LyC emitters.