arXiv subjects

Genoveva Micheva

Publications and source records attributed to Genoveva Micheva.

At least 19 recordsLinked to original sources

arXiv2024

SatHub Panel: Satellite Interference in Observatories Around the World

Satellite constellation interference occurs across astronomical disciplines. We present examples of interference from radio and $γ$-Ray astronomy to optical and spectroscopic interference in ground-based and space-borne facilities. In particular, we discuss the impact of artificial satellites on the Hubble Space Telescope (HST), the High Energy Stereoscopic System (H.E.S.S.), an Imaging Atmospheric Cherenkov Telescope, as well as possible mitigation strategies for the European Southern Observatory 4-metre Multi-Object Spectrograph Telescope (ESO 4MOST). Furthermore, we shed light on how ground-based optical telescopes such as the Oukaimeden Observatory contribute to IAU Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference (IAU CPS) efforts that quantify satellite brightness.

astro-ph.IM↗

arXiv2023

Precision spectrophotometry for PNLF distances: the case of NGC 300

The Multi-Unit Spectroscopic Explorer (MUSE) has enabled a renaissance of the planetary nebula luminosity function (PNLF) as a standard candle. In the case of NGC 300, we learned that the precise spectrophotometry of MUSE was crucial to obtain an accurate PNLF distance. We present the advantage of the integral field spectrograph compared to the slit spectrograph in delivering precise spectrophotometry by simulating a slit observation on integral field spectroscopy data. We also discuss the possible systematic shift in measuring the PNLF distance using the least-square method, especially when the PNLF cutoff is affected by small number statistics.

astro-ph.GA↗

arXiv2023

UM462, a local green pea galaxy analogue under the MUSE magnifying glass

[ABRIDGED] Stellar feedback in high-redshift galaxies plays an important role in the re-ionization epoch of the Universe. Green Pea galaxies (GPs) postulate as favorite local laboratories. However, at their typical redshift of $z\sim0.2$, the most intimate interaction between stars and surrounding ISM cannot be disentangled. Detailed studies of Blue Compact Dwarf galaxies (BCDs) are necessary to anchor our investigations on them. We present here a study in detail UM 462, a BCD with similar properties to GPs uisng high quality optical IFS data with MUSE. Total oxygen abundance by means of the direct method is 12+$\log$(O/H)$\sim$8.02 and homogenous all over the galaxy, in stark contrast with the metallicities derived from several strong line methods. The velocity field for the ionised gas presents a velocity stratification in the area towards the north with redder velocities in the high ionisation lines and bluer velocities in the low ionisation lines. This is the only area with velocity dispersions clearly above the MUSE instrumental width, and it is surrounded by two $\sim$1 kpc-long structures nicknamed \emph{the horns}. We interpret the observational evidence in that area as a fragmented super-bubble fruit of the stellar feedback and it may constitute a preferred channel for LyC photons from the youngest generation of stars to escape. The most recent SF seems to propagate from the outer to the inner parts of the galaxy, and then from east to west. We identified a supernova remnant and Wolf-Rayet stars - as traced by the red bump - that support this picture. The direction of the propagation implies the presence of younger Wolf-Rayet stars at the maximum in H$α$. The ensemble of results exemplifies the potential of 2D detailed spectroscopic studies of dwarf star-forming galaxies at high spatial resolution as key reference for similar studies on primeval galaxies.

astro-ph.GA↗

arXiv2023

MUSE crowded field 3D spectroscopy in NGC 300 : IV. Planetary nebula luminosity function

We perform a deep survey of planetary nebulae (PNe) in the spiral galaxy NGC 300 to construct its planetary nebula luminosity function (PNLF). We aim to derive the distance using the PNLF and to probe the characteristics of the most luminous PNe. We analyse 44 fields observed with MUSE at the VLT, covering a total area of $\sim11$ kpc$^2$. We find [OIII]5007 sources using the differential emission line filter (DELF) technique. We identify PNe through spectral classification using the aid of the BPT-diagram. The PNLF distance is derived using the maximum likelihood estimation technique. For the more luminous PNe, we also measure their extinction using the Balmer decrement. We estimate the luminosity and effective temperature of the central stars of the luminous PNe, based on estimates of the excitation class and the assumption of optically thick nebulae. We identify 107 PNe and derive a most-likely distance modulus $(m-M)_0 = 26.48^{+0.11}_{-0.26}$ ($d = 1.98^{+0.10}_{-0.23}$ Mpc). We find that the PNe at the PNLF cut-off exhibit relatively low extinction, with some high extinction cases caused by local dust lanes. We present the lower limit luminosities and effective temperatures of the central stars for some of the brighter PNe. We also identify a few Type I PNe that come from a young population with progenitor masses $>2.5 \, M_\odot$, however do not populate the PNLF cut-off. The spatial resolution and spectral information of MUSE allow precise PN classification and photometry. These capabilities also enable us to resolve possible contamination by diffuse gas and dust, improving the accuracy of the PNLF distance to NGC 300.

astro-ph.GA↗

arXiv2022

MUSE crowded field 3D spectroscopy in NGC 300 III. Characterizing extremely faint HII regions and diffuse ionized gas

There are known differences between the physical properties of HII and diffuse ionized gas (DIG), but most of the studied regions in the literature are relatively bright. We compiled a faint sample of 390 HII regions with median $\log_{10}Hα$=34.7 in the spiral galaxy NGC300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the DIG. We used MUSE data of nine fields in NGC300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm regions. We binned the data in dendrogram leaves and extracted all strong nebular emission lines. We identified HII and DIG regions and compared their electron densities, metallicity, extinction, and kinematic properties. We also tested the effectiveness of unsupervised machine-learning algorithms in distinguishing between the HII and DIG regions. The gas density in the HII and DIG regions is close to the low-density limit in all fields. The average velocity dispersion in the DIG is higher than in the HII regions, which can be explained by the DIG being 1.8 kK hotter than HII gas. The DIG manifests a lower ionization parameter than HII gas, and the DIG fractions vary between 15-77%, with strong evidence of a contribution by hot low-mass evolved stars and shocks to the DIG ionization. Most of the DIG is consistent with no extinction and an oxygen metallicity that is indistinguishable from that of the HII gas.We observe a flat metallicity profile in the central region, without a sign of a gradient. The differences between extremely faint HII and DIG regions follow the same trends and correlations as their much brighter cousins. HII and DIG are so heterogeneous, however, that the differences within each class are larger than the differences between the two classes.

astro-ph.GA↗

arXiv2022

The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics

The Lyman continuum (LyC) cannot be observed at the epoch of reionization (z {\gtrsim} 6) due to intergalactic H I absorption. To identify Lyman continuum emitters (LCEs) and infer the fraction of escaping LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Lyα, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [O III]/[O II] flux ratio and star formation rate surface density, predict whether a galaxy is a LCE. The relationship between these galaxy properties and the fraction of escaping LyC flux suggests that LyC escape depends strongly on H I column density, ionization parameter, and stellar feedback. We find LCEs occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of LyC escape.

astro-ph.GA↗

arXiv2022

The Low-Redshift Lyman Continuum Survey I: New, Diverse Local Lyman-Continuum Emitters

The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the epoch of reionization is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with HST/COS for a z=0.2-0.4 sample of 66 galaxies. After careful processing of the FUV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.

astro-ph.GA↗

arXiv2021

Ionizing radiation from AGNs at z>3.3 with the Subaru Hyper Suprime-Cam Survey and the CFHT Large Area U-band Deep Survey (CLAUDS)

We use deep and wide imaging data from the CFHT Large Area U-band Deep Survey (CLAUDS) and the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) to constrain the ionizing radiation (Lyman Continuum; LyC) escape fraction from AGNs at $z \sim 3 - 4$. For 94 AGNs with spectroscopic redshifts at $3.3 < z < 4.0$, we use their U-band / i-band flux ratios to estimate LyC transmission of individual AGNs. The distribution of their LyC transmission shows values lower than the range of LyC transmission values for IGM of the same redshift range, which suggests that LyC escape fraction of AGNs at $z>3.3$ is considerably lower than unity in most cases. We do not find any trend in LyC transmission values depending on their UV luminosities. Based on the photometry of stacked images we find the average flux ratio of LyC and non-ionizing UV photons escaping from the objects $(f_{LyC}/f_{UV})^{out} = 0.182 \pm 0.043$ for AGNs at $3.3<z<3.6$, which corresponds to LyC escape fraction $f_{esc} = 0.303 \pm 0.072$ if we assume a fiducial intrinsic SED of AGN. Based on the estimated LyC escape fraction and the UV luminosity function of AGNs, we argue that UV-selected AGNs' contribution to the LyC emissivity at the epoch is minor, although the size of their contribution largely depends on the shape of the UV luminosity function.

astro-ph.GA↗

arXiv2021

Limits to Ionization-Parameter Mapping as a Diagnostic of HII Region Optical Depth

We employ ionization-parameter mapping (IPM) to infer the optical depth of HII regions in the northern half of M33. We construct [OIII]$λ5007$/[OII]$λ3727$ and [OIII]$λ5007$/[SII]$λ6724$ ratio maps from narrow-band images continuum-subtracted in this way, from which we classify the HII regions by optical depth to ionizing radiation, based on their ionization structure. This method works relatively well in the low metallicity regime, $12 + \log(\rm O/H) \leq 8.4$, where [OIII]$λ\lambda4949,5007$ is strong. However, at higher metallicities, the method breaks down due to the strong dependence of the [OIII]$λ\lambda4959,5007$ emission lines on the nebular temperature. Thus, although O$^{++}$ may be present in metal-rich HII regions, these commonly used emission lines do not serve as a useful indicator of its presence, and hence, the O ionization state. In addition, IPM as a diagnostic of optical depth is limited by spatial resolution. We also report a region of highly excited [OIII] extending over an area $\sim$ 1 kpc across and [OIII]$\lambda5007$ luminosity of $4.9\pm 1.5\times10^{38}$ erg/s, which is several times higher than the ionizing budget of any potential sources in this portion of the galaxy. Finally, this work introduces a new method for continuum subtraction of narrow-band images based on the dispersion of pixels around the mode of the diffuse-light flux distribution. In addition to M33, we demonstrate the method on C III]$λ$1909 imaging of Haro~11, ESO 338-IG004, and Mrk~71.

astro-ph.GA↗

arXiv2021

The source of leaking ionizing photons from Haro11 -- Clues from HST/COS spectroscopy of knots A, B and C

Understanding the escape of ionizing (Lyman continuum) photons from galaxies is vital for determining how galaxies contributed to reionization in the early universe. While directly detecting Lyman continuum from high redshift galaxies is impossible due to the intergalactic medium, low redshift galaxies in principle offer this possibility, but requirie observations from space. The first local galaxy for which Lyman continuum escape was found is Haro11 , a luminous blue compact galaxy at z=0.02, where observations with the FUSE satellite revealed an escape fraction of 3.3 %. However the FUSE aperture covers the entire galaxy, and it is not clear from where the Lyman continuum is leaking out. Here we utilize HST/COS spectroscopy in the wavelength range 1100-1700 A of the three knots (A, B, and C) of Haro11 to study the presence of Ly-$α$ emission and the properties of intervening gas. We find that all knots have bright Ly-$α$ emission. UV absorption lines, originating in the neutral interstellar medium, as well as lines probing the ionized medium, are seen extending to blue shifted velocities of 500 km/s in all three knots, demonstrating the presence of an outflowing multiphase medium. We find that knots A and B have large covering fractions of neutral gas, making LyC escape along these sightlines improbable, while knot C has a much lower covering fraction ($\lesssim50$%). Knot C also has the the highest Ly-$α$ escape fraction and we conclude that it is the most likely source of the escaping Lyman continuum detected in Haro11.

astro-ph.GA↗

arXiv2020

Wide Field Spectral Imaging with Shifted Excitation Raman Difference Spectroscopy Using the Nod and Shuffle Technique

Wide field Raman imaging using the integral field spectroscopy approach was used as a fast, one shot imaging method for the simultaneous collection of all spectra composing a Raman image. For the suppression of autofluorescence and background signals such as room light, shifted excitation Raman difference spectroscopy (SERDS) was applied to remove background artifacts in Raman spectra. To reduce acquisition times in wide field SERDS imaging, we adapted the nod and shuffle technique from astrophysics and implemented it into a wide field SERDS imaging setup. In our adapted version, the nod corresponds to the change in excitation wavelength, whereas the shuffle corresponds to the shifting of charges up and down on a Charge-Coupled Device (CCD) chip synchronous to the change in excitation wavelength. We coupled this improved wide field SERDS imaging setup to diode lasers with 784.4/785.5 and 457.7/458.9 nm excitation and applied it to samples such as paracetamol and aspirin tablets, polystyrene and polymethyl methacrylate beads, as well as pork meat using multiple accumulations with acquisition times in the range of 50 to 200 ms. The results tackle two main challenges of SERDS imaging: gradual photobleaching changes the autofluorescence background, and multiple readouts of CCD detector prolong the acquisition time.

physics.ins-det↗

arXiv2020

Spatially resolved CIII]$λ$1909 emission in Haro 11

The CIII]1909 (hereafter, C III]) line is the strongest ultraviolet emission line after Ly$α$ and is therefore of interest to high redshift studies of star-forming (SF) galaxies near the epoch of reionization. It is thought that C III] emission is strongest in galaxies with subsolar metallicity and low mass, however, spectral observations of numerous such galaxies at high and low redshift produce inconclusive or even contradictory results. We present the first ever C III ] imaging, obtained with HST/STIS for the low-redshift SF galaxy Haro 11. Cluster parameters like stellar mass, dust fraction and dust attenuation, and ionization parameter, obtained through spectral energy distribution fitting, show no correlation with the CIII] equivalent width (EW), which may be due to a combination of the limitation of the models and the age-homogeneity of the cluster population. Comparing the ratio of C III] emission line flux from individual clusters to that of H$α$, [O III], and [O II] we find that the clusters with the highest EW(C III]) can be reconciled only with Cloudy models with an extremely high C/O ratio of $\ge$ 1.4(C/O)$_\odot$ for an ionizing population of single stars, binary stars, or a mixture of binary stars and active galactic nuclei. Given the point-like nature of strong C III], the integrated total strength of EW(C III]) becomes dependent on the morphology of the galaxy, which would explain the large scatter in EW(C III]) strengths, observed in galaxies with otherwise similar SF properties, and of similarly low metallicity and stellar mass.

astro-ph.GA↗

arXiv2020

Testing an indirect method for identifying galaxies with high levels of Lyman continuum leakage

Using a sample of galaxies at $z\approx 3$ with detected Lyman Continuum (LyC) leakage in the SSA22 field, we attempt to verify a proposed indirect method for identifying cases with high LyC escape fraction $f_\mathrm{esc}$ based on measurements of the H$β$ equivalent width (EW) and the $β$ slope of the UV continuum. To this end, we present Keck/MOSFIRE H$β$ emission line flux measurements of LyC galaxies (LCGs) at spectroscopic redshifts $z_{\mathrm{spec}} \sim 3.3$, Lyman break galaxies (LBGs) at photometric redshifts $z_{\mathrm{phot}} = 2.7$--$3.7$, and Ly$α$ emitters at $z_{\mathrm{phot}} = 3.1$. We also reconfirm the spectroscopic redshifts and measure the H$β$ emission line fluxes from 2 LCGs and 6 LBGs. For the LCG in our sample with the most extreme $f_\mathrm{esc}$, as revealed by the direct detection of LyC photons, we find that the EW(H$β$)--$β$ method gives a broadly consistent estimate for $f_\mathrm{esc}$, although the error bars remain very large. We also discuss how a combination of $f_\mathrm{esc}$ measurements based on direct and indirect methods can shed light on the LyC escape mechanism and the anisotropy of the leakage.

astro-ph.GA↗

arXiv2019

Subaru narrow-band imaging search for Lyman continuum from galaxies at z>3 in the GOODS-N field

We report results of a search for galaxies at z>3 with Lyman continuum (LyC) emission using a narrow-band filter NB359 with Subaru / Suprime-Cam in a ~800 arcmin$^2$ blank field around the GOODS-N. We use 103 star-forming galaxies (SFGs) and 8 AGNs with spectroscopic redshifts in a range between 3.06 and 3.5, and 157 photometrically selected z=3.1 Lyman $α$ emitter (LAE) candidates as the targets. After removing galaxies spectroscopically confirmed to be contaminated by foreground sources, we found two SFGs and one AGN as candidate LyC emitting sources among the targets with spectroscopic redshifts. Among LAE candidates, five sources are detected in the NB359 image, and three among them may be contaminated by foreground sources. We compare the sample galaxies in the GOODS-N with those in the SSA22, where a prominent protocluster at z=3.1 is known and the LyC search using the same NB359 filter has been made. Frequency of galaxies with LyC leakage in the SSA22 field may be about two times higher than the galaxies in the GOODS-N with the sample UV magnitude range, although the numbers of LyC detections in these fields are too small to make a statistically significant conclusion. By combining the sample galaxies in these fields, we place the 3$σ$ upper limits of the observed LyC-to-UV flux density ratio and LyC escape fraction for galaxies at z=3.1 with absolute UV magnitude $M_{UV} < -18.8$ as ($f_{LyC}/f_{UV})_{obs} < 0.036$ and $f_{esc}^{abs}<8$\%, respectively.

astro-ph.GA↗

arXiv2019

An IFU investigation of possible Lyman continuum escape from Mrk 71/NGC 2366

Mrk 71/NGC 2366 is the closest Green Pea (GP) analog and candidate Lyman Continuum (LyC) emitter. Recently, 11 LyC-leaking GPs have been detected through direct observations of the ionizing continuum, making this the most abundant class of confirmed LyC-emitters at any redshift. High resolution, multi-wavelength studies of GPs can lead to an understanding of the method(s), through which LyC escapes from these galaxies. The proximity of Mrk 71/NCG 2366 offers unprecedented detail on the inner workings of a GP analog, and enables us to identify the mechanisms of LyC escape. We use 5825-7650Å integral field unit PMAS observations to study the kinematics and physical conditions in Mrk 71. An electron density map is obtained from the [S II] ratio. A fortuitous second order contamination by the [O II]3727 doublet enables the construction of an electron temperature map. Resolved maps of sound speed, thermal broadening, "true" velocity dispersion, and Mach number are obtained and compared to the high resolution magneto-hydrodynamic SILCC simulations. Two regions of increased velocity dispersion indicative of outflows are detected to the north and south of the super star cluster, knot B, with redshifted and blueshifted velocities, respectively. We confirm the presence of a faint broad kinematical component, which is seemingly decoupled from the outflow regions, and is fainter and narrower than previously reported in the literature. Within uncertainties, the low- and high-ionization gas move together. Outside of the core of Mrk 71, an increase in Mach numbers is detected, implying a decrease in gas density. Simulations suggest this drop in density can be as high as ~4 dex, down to almost optically thin levels, which would imply a non-zero LyC escape fraction along the outflows... [abridged]

astro-ph.GA↗

arXiv2018

Mapping Lyman Continuum escape in Tololo 1247-232

Low redshift, spatially resolved Lyman continuum (LyC) emitters allow us to clarify the processes for LyC escape from these starburst galaxies. We use Hubble Space Telescope (HST) WFC3 and ACS imaging of the confirmed low-redshift LyC emitter Tol 1247-232 to study the ionization structure of the gas and its relation to the ionizing star clusters. We perform ionization parameter mapping (IPM) using [O III]4959, 5007 and [O II]3727 imaging as the high- and low-ionization tracers, revealing broad, large-scale, optically thin regions originating from the center, and reaching the outskirts of the galaxy, consistent with LyC escape. We carry out stellar population synthesis modeling of the 26 brightest clusters using our HST photometry. Combining these data with the nebular photometry, we find a global LyC escape fraction of f_esc = 0.12, with uncertainties also consistent with zero escape and with all measured f_esc values for this galaxy. Our analysis suggests that, similar to other candidate LyC emitters, a two-stage starburst has taken place in this galaxy, with a 12 Myr old, massive, central cluster likely having pre-cleared regions in and around the center, and the second generation of 2 - 4 Myr old clusters dominating the current ionization, including some escape from the galaxy.

astro-ph.GA↗

arXiv2018

The Lyman Alpha Reference Sample IX: Revelations from deep surface photometry

The Lyman Alpha Reference Sample (LARS) of 14 star-forming galaxies offers a wealth of insight into the workings of these local analogs to high-redshift star-forming galaxies. The sample has been well-studied in terms of LyA and other emission line properties, such as HI mass, gas kinematics, and morphology. We analyze deep surface photometry of the LARS sample in UBIK broadband imaging obtained at the Nordic Optical Telescope and the Canada-France-Hawaii Telescope, and juxtaposition their derived properties with a sample of local high-redshift galaxy analogs, namely, with blue compact galaxies (BCGs). We construct radial surface brightness and color profiles with both elliptical and isophotal integration, as well as RGB images, deep contours, color maps, a burst fraction estimate, and a radial mass-to-light ratio profile for each LARS galaxy. Standard morphological parameters like asymmetry, clumpiness, the Gini and M20 coefficients are [...] analyzed, as well as isophotal asymmetry profiles for each galaxy. [...] We compare the LARS to the properties of the BCG sample and highlight the differences. Several diagnostics indicate that the LARS galaxies have highly disturbed morphologies even at the level of the faintest isophotes [...]. The ground-based photometry [...] reveals previously unexplored isophotes [...]. The burst fraction estimate suggests a spatially more extended burst region in LARS than in the BCGs. [...] The galaxies in the LARS sample appear to be in earlier stages of a merger event compared to the BCGs. Standard morphological diagnostics like asymmetry, clumpiness, Gini and M20 coefficients cannot separate the two samples, although an isophotal asymmetry profile successfully captures the average difference in morphology. These morphological diagnostics do not show any correlation with the equivalent width or the escape fraction of Lyman Alpha. [abridged]

astro-ph.GA↗

arXiv2017

Dense CO in Mrk 71-A: Superwind Suppressed in a Young Super Star Cluster

We report the detection of CO(J=2-1) coincident with the super star cluster (SSC) Mrk 71-A in the nearby Green Pea analog galaxy, NGC 2366. Our NOEMA observations reveal a compact, ~7 pc, molecular cloud whose mass (10^5 M_sun) is similar to that of the SSC, consistent with a high star-formation efficiency, on the order of 0.5. There are two, spatially distinct components separated by 11 km/s. If expanding, these could be due to momentum-driven, stellar wind feedback. Alternatively, we may be seeing the remnant infalling, colliding clouds responsible for triggering the SSC formation. The kinematics are also consistent with a virialized system. These extreme, high-density, star-forming conditions inhibit energy-driven feedback; the co-spatial existence of a massive, molecular cloud with the SSC supports this scenario, and we quantitatively confirm that any wind-driven feedback in Mrk 71-A is momentum-driven, rather than energy-driven. Since Mrk 71-A is a candidate Lyman continuum emitter, this implies that energy-driven superwinds may not be a necessary condition for the escape of ionizing radiation. In addition, the detection of the nebular continuum emission yields an accurate astrometric position for the Mrk 71-A. We also detect four other massive, molecular clouds in this giant star-forming complex.

astro-ph.GA↗