arXiv subjects

Genoveva Micheva

Publications and source records attributed to Genoveva Micheva.

26 records · Page 2Linked to original sources

arXiv2017

Mrk 71/NGC 2366: The nearest Green Pea analog

We present the remarkable discovery that the dwarf irregular galaxy NGC 2366 is an excellent analog of the Green Pea (GP) galaxies, which are characterized by extremely high ionization parameters. The similarities are driven predominantly by the giant H II region Markarian 71 (Mrk 71). We compare the system with GPs in terms of morphology, excitation properties, specific star-formation rate, kinematics, absorption of low-ionization species, reddening, and chemical abundance, and find consistencies throughout. Since extreme GPs are associated with both candidate and confirmed Lyman continuum (LyC) emitters, Mrk 71/NGC 2366 is thus also a good candidate for LyC escape. The spatially resolved data for this object show a superbubble blowout generated by mechanical feedback from one of its two super star clusters (SSCs), Knot B, while the extreme ionization properties are driven by the <1 Myr-old, enshrouded SSC Knot A, which has ~ 10 times higher ionizing luminosity. Very massive stars (> 100 Msun) may be present in this remarkable object. Ionization-parameter mapping indicates the blowout region is optically thin in the LyC, and the general properties also suggest LyC escape in the line of sight. Mrk 71/NGC 2366 does differ from GPs in that it is 1 - 2 orders of magnitude less luminous. The presence of this faint GP analog and candidate LyC emitter (LCE) so close to us suggests that LCEs may be numerous and commonplace, and therefore could significantly contribute to the cosmic ionizing budget. Mrk 71/NGC 2366 offers an unprecedentedly detailed look at the viscera of a candidate LCE, and could clarify the mechanisms of LyC escape.

astro-ph.GA↗

arXiv2016

Searching for candidates of Lyman continuum sources - revisiting the SSA22 field

We present the largest to date sample of hydrogen Lyman continuum (LyC) emitting galaxy candidates at any redshift, with 18 Ly$α$ Emitters (LAEs) and 7 Lyman Break Galaxies (LBGs), obtained from the SSA22 field with Subaru/Suprime-Cam. The sample is based on the 159 LAEs and 136 LBGs observed in the field, all with spectroscopically confirmed redshifts, and these LyC candidates are selected as galaxies with counterpart in a narrow-band filter image which traces LyC at $z\geq 3.06$. Many LyC candidates show a spatial offset between the rest-frame non-ionizing ultraviolet (UV) detection and the LyC-emitting substructure or between the Ly$α$ emission and LyC. The possibility of foreground contamination complicates the analysis of the nature of LyC emitters, although statistically it is highly unlikely that all candidates in our sample are contaminated by foreground sources. Many viable LyC LAE candidates have flux density ratios inconsistent with standard models, while also having too blue UV slopes to be foreground contaminants. Stacking reveals no significant LyC detection, suggesting that there is a dearth of objects with marginal LyC signal strength, perhaps due to a bimodality in the LyC emission. The foreground contamination-corrected $3σ$ upper limits of the observed average flux density ratios are $f_{LyC}/f_{UV}<0.08$ from stacking LAEs and $f_{LyC}/f_{UV}<0.02$ from stacking LBGs. There is a sign of a positive correlation between LyC and Ly$α$, suggesting that both types of photons escape via a similar mechanism. The LyC detection rate among proto-cluster LBGs is seemingly lower compared to the field.

astro-ph.GA↗

arXiv2016

Lyman continuum leaking AGN in the SSA22 field

Subaru/SuprimeCam narrowband photometry of the SSA22 field reveals the presence of four Lyman continuum (LyC) candidates among a sample of 14 AGN. Two show offsets and likely have stellar LyC in nature or are foreground contaminants. The remaining two LyC candidates are Type I AGN. We argue that the average LyC escape fraction of high redshift low luminosity AGN is not likely to be unity, as often assumed in the literature. From direct measurement we obtain the average LyC-to-UV flux density ratio and ionizing emissivity for a number of AGN classes and find it at least a factor of two lower than values obtained assuming f_esc = 1. Comparing to recent Lyα forest measurements, AGNs at redshift z~3 make up at most ~12% and as little as ~5% of the total ionizing budget. Our results suggest that AGNs are unlikely to dominate the ionization budget of the Universe at high redshifts.

astro-ph.GA↗

arXiv2014

The Lyman-alpha Reference Sample: I. Survey outline and first results for Markarian 259

The Lyman-alpha reference sample (LARS) is a program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the astrophysics of the visibility and strength of the Lyman-alpha (Lya) line of hydrogen. This article presents an overview of the survey, its selection function and HST imaging observations. The sample was selected from the GALEX+SDSS catalogue at z=0.028-0.19, in order to allow Lya to be captured with combinations of long pass filters in the Solar Blind Channel (SBC) of HST/ACS. In addition, LARS utilises Halpha and Hbeta narrow, and U, B, i broad-band imaging with ACS and WFC3. In order to study galaxies in which large numbers of Lya photons are produced we demanded an Halpha equivalent width > 100Å. The sample of 14 galaxies covers far UV (FUV) luminosities that overlaps with those of high-z Lya emitters and Lyman Break Galaxies (LBGs). We present the reduction steps used to obtain the Lya images, including our LARS eXtraction software (LaXs) which utilises pixel-by-pixel spectral synthesis fitting to subtract the continuum at Lya. We demonstrate that the use of SBC long pass filters dramatically increase the signal to noise compared to the nominal Lya filter in SBC. To exemplify, we present results for Mrk 259. This irregular galaxy shows extended but strongly asymmetric Lya emission. Spectroscopy from HST/COS show a moderate outflow in the neutral ISM and an asymmetric Lya profile. Radiative transfer modeling is able to reproduce the Lya line profile, confirming the presence of an outflow. The integrated photometry provides a Lya luminosity of 1.3E42 erg/s an equivalent width W(Lya) =45Å and a FUV absolute magnitude -19.2. Mrk 259 would hence be detectable in high-z Lya and LBG surveys. The total Lya escape fraction is 12%, similar to that observed at z>4. (shortened)

astro-ph.GA↗

arXiv2012

Deep multiband surface photometry on star forming galaxies: II. A volume limited sample of 21 emission lines galaxies

We present deep surface photometry of a volume--limited sample of 21 UM emission line galaxies in broadband optical UBVRI and near infra-red (NIR) HKs filters. The sample comprises 19 blue compact galaxies (BCGs) and two spirals. For some targets the exposure times are the deepest to date. For the BCG UM462 we observe a previously undetected second disk component beyond a surface brightness level of mu_B=26 mag arcsec^{-2}. This is a true low surface brightness component with central surface brightness mu_0=24.1 mag arcsec^{-2} and scale length h_r=1.5 kpc. All BCGs are dwarfs, with M_B>=-18, and very compact, with an average scale length of h_r~1 kpc. We separate the burst and host populations for each galaxy and compare them to stellar evolutionary models with and without nebular emission contribution. We also measure the A_{180} asymmetry in all filters and detect a shift from optical to NIR in the average asymmetry of the sample. This shift seems to be correlated with the morphological class of the BCGs. Using the color-asymmetry relation, we identify five BCGs in the sample as mergers, which is confirmed by their morphological class. Though clearly separated from normal galaxies in the concentration-asymmetry parameter space, we find that it is not possible to distinguish luminous starbursting BCGs from the merely star forming low luminosity BCGs.

astro-ph.CO↗

arXiv2012

Deep multiband surface photometry on star forming galaxies: I. A sample of 24 blue compact galaxies

[Abridged] We present deep optical and near-infrared UBVRIHKs imaging data for 24 blue compact galaxies (BCGs). The sample contains luminous dwarf and intermediate-mass BCGs which are predominantly metal-poor, although a few have near-solar metallicities. We have analyzed isophotal and elliptical integration surface brightness and color profiles, extremely deep (mu_B<29 mag arcsec^{-2}) contour maps and RGB images for each galaxy in the sample. The colors are compared to different spectral evolutionary models. We detect extremely extended low surface brightness (LSB) components dominant beyond the Holmberg radius as well as optical bridges between companion galaxies at the mu_V~28th mag arcsec^{-2} isophotal level. The central surface brightness mu_0 and scale length h_r are derived from two radial ranges typically assumed to be dominated by the underlying host galaxy. We find that mu_0 and h_r of the BCGs host deviate from those of dwarf ellipticals (dE) and dwarf irregulars (dI) solely due to a strong burst contribution to the surface brightness profile almost down to the Holmberg radius. Structural parameters obtained from a fainter region, mu_B=26-28 mag arcsec^{-2}, are consistent with those of true LSB galaxies for the starbursting BCGs in our sample, and with dEs and dIs for the BCGs with less vigorous star formation.

astro-ph.CO↗

arXiv2010

The faint outskirts of the blue compact galaxy Haro 11: is there a red excess?

Previous studies of the low surface brightness host of the blue compact galaxy (BCG) Haro 11 have suggested an abnormally red color of V-K=4.2+-0.8 for the host galaxy. This color is inconsistent with any normal stellar population over a wide range of stellar metallicities (Z=0.001-0.02). Similar though less extreme host colors have been measured for other BCGs and may be reconciled with population synthesis models, provided that the stellar metallicity of the host is higher than that of the ionized gas in the central starburst. We present the deepest V and K band observations to date of Haro 11 and derive a new V-K color for the host galaxy. Our new data suggest a far less extreme colour of V-K=2.3+-0.2, which is perfectly consistent with the expectations for an old host galaxy with the same metallicty as that derived from nebular emission lines in the star-forming center.

astro-ph.CO↗

arXiv2009

Deep V and K band photometry of the host galaxy of Haro 11

Previous studies of the host galaxy of Haro 11 have suggested an extreme red color of V-K=4.2+-0.8 which cannot be reconciled with any normal stellar population of reasonable metallicity. We present the deepest V and K band data to date of the blue compact galaxy (BCG) Haro 11 and derive a new V-K color for the host. Our new data suggest a much more modest value of V-K=2.3+-0.2, which is in the same range as V-K colors measured for several other BCGs. The new Haro 11 color is not abnormally red and can be attributed to an old metal-poor stellar population with a Salpeter initial mass function.

astro-ph.CO↗