[en] We analyze the intrinsic flux ratios of various visible–near-infrared filters with respect to 3.5 μm for simple and composite stellar populations (CSPs), and their dependence on age, metallicity, and star formation history (SFH). UV/optical light from stars is reddened and attenuated by dust, where different sightlines across a galaxy suffer varying amounts of extinction. Tamura et al. (2009) developed an approximate method to correct for dust extinction on a pixel-by-pixel basis, dubbed the “${\mathrm{\beta <!--\; ??\; -->}}_V$” method, by comparing the observed flux ratio to an empirical estimate of the intrinsic ratio of visible and ∼3.5 μm data. Through extensive modeling, we aim to validate the “${\mathrm{\beta <!--\; ??\; -->}}_V$” method for various filters spanning the visible through near-infrared wavelength range, for a wide variety of simple and CSPs. Combining Starburst99 and BC03 models, we built spectral energy distributions (SEDs) of simple (SSP) and composite (CSP) stellar populations for various realistic SFHs, while taking metallicity evolution into account. We convolve various 0.44–1.65 μm filter throughput curves with each model SED to obtain intrinsic flux ratios ${\mathrm{\beta <!--\; ??\; -->}}_{\mathrm{\lambda <!--\; ??\; -->},0}$. When unconstrained in redshift, the total allowed range of ${\mathrm{\beta <!--\; ??\; -->}}_{V,0}$ is 0.6–4.7, or almost a factor of eight. At known redshifts, and in particular at low redshifts (z ≲ 0.01), ${\mathrm{\beta <!--\; ??\; -->}}_{V,0}$ is predicted to span a narrow range of 0.6–1.9, especially for early-type galaxies (0.6–0.7), and is consistent with observed ${\mathrm{\beta <!--\; ??\; -->}}_V$ values. The ${\mathrm{\beta <!--\; ??\; -->}}_{\mathrm{\lambda <!--\; ??\; -->}}$ method can therefore serve as a first-order dust-correction method for large galaxy surveys that combine JWST (rest-frame 3.5 μm) and HST (rest-frame visible–near-IR) data.

[en] Recent Hubble Space Telescope (HST) observations of the extragalactic radio source Centaurus A (Cen A) display a young stellar population around the southwest tip of the inner filament 8.5 kpc from the galactic center of Cen A, with ages in the range 1–3 Myr. Crockett et al. have argued that the transverse bow shock of the Cen A jet triggered this star formation as it impacted dense molecular cores of clouds in the filament. To test this hypothesis, we perform three-dimensional numerical simulations of star formation induced by the jet bow shock in the inner filament of Cen A, using a positivity-preserving, weighted, essentially non-oscillatory method to solve the equations of gas dynamics with radiative cooling. We find that star clusters form inside a bow-shocked molecular cloud when the maximum initial density of the cloud is $⩾<!--\; ???\; -->40$ H₂ molecules cm⁻³. In a typical molecular cloud of mass ${10}^6{M}_{\odot <!--\; ???\; -->}$ and diameter 200 pc, approximately 20 star clusters of mass ${10}^4{M}_{\odot <!--\; ???\; -->}$ are formed, matching the HST images.

[en] We have extracted point-spread-function-fitted stellar photometry from near-ultraviolet, optical, and near-infrared images, obtained with the Hubble Space Telescope, of the nearby (D ∼ 5.5 Mpc) SBm galaxy NGC 1311. The ultraviolet and optical data reveal a population of hot main-sequence (MS) stars with ages of 2-10 Myr. We also find populations of blue supergiants with ages between 10 and 40 Myr and red supergiants with ages between 10 and 100 Myr. Our near-infrared data show evidence of star formation going back ∼1 Gyr, in agreement with previous work. Fits to isochrones indicate a metallicity of Z ∼ 0.004. The ratio of blue to red supergiants is consistent with this metallicity. This indicates that NGC 1311 follows the well-known luminosity-metallicity relation for late-type dwarf galaxies. About half of the hot MS stars and blue supergiants are found in two regions in the inner part of NGC 1311. These two regions are each about 200 pc across, and thus have crossing times roughly equal to the 10 Myr age we find for the dominant young population. The luminosity functions of the supergiants indicate a slowly rising star formation rate (∼10^-3 M_sun yr^-1) from ∼100 Myr ago until ∼15 Myr ago, followed by a strong enhancement (∼10^-2 M_sun yr^-1) at ∼10 Myr ago. We see no compelling evidence for gaps in the star-forming history of NGC 1311 over the last 100 Myr, and, with lower significance, none over the last Gyr. This argues against a bursting mode, and in favor of a gasping or breathing mode for the recent star formation history.

[en] Lyα blobs-luminous, spatially extended emission-line nebulae, often lacking bright continuum counterparts-are common in dense environments at high redshift. Until recently, atmospheric absorption and filter technology have limited our knowledge of any similar objects at z ≤ 2. We use Galaxy Evolution Explorer slitless spectroscopy to search for similar objects in the rich environments of two known cluster and supercluster fields at z = 0.8, where the instrumental sensitivity peaks. The regions around Cl 1054-0321 and Cl 0023+0423 were each observed in slitless-spectrum mode for 10-19 ks, with accompanying direct images of 3-6 ks to assist in recognizing continuum sources. Using several detection techniques, we find no resolved Lyα emitters to a flux limit of (1.5-9) x 10^-15 erg cm^-2 s^-1, on size scales of 5-30 arcsec. This corresponds to line luminosities of (0.5-3) x 10⁴³ erg s^-1 for linear scales 35-200 kpc. Comparison with both blind and targeted surveys at higher redshifts indicates that the population must have evolved in comoving density at least as strongly as (1 + z)³. These results suggest that the population of Lyα blobs is specific to the high-redshift universe.

[en] We apply Bayesian statistics with prior probabilities of galaxy surface luminosity (SL) to improve photometric redshifts. We apply the method to a sample of 1266 galaxies with spectroscopic redshifts in the GOODS North and South fields at 0.1 ∼< z ∼< 2.0. We start with spectrophotometric redshifts (SPZs) based on Probing Evolution and Reionization Spectroscopically grism spectra, which cover a wavelength range of 6000-9000 A, combined with (U)BViz(JHK) broadband photometry in the GOODS fields. The accuracy of SPZ redshifts is estimated to be σ(Δ(z)) = 0.035 with an systematic offset of -0.026, where Δ(z) = Δz/(1 + z), for galaxies in redshift range of 0.5 ∼< z ∼< 1.25. The addition of the SL prior probability helps break the degeneracy of SPZ redshifts between low redshift 4000 A break galaxies and high-redshift Lyman break galaxies which are mostly catastrophic outliers. For the 1138 galaxies at z ∼< 1.6, the fraction of galaxies with redshift deviation Δ(z)>0.2 is reduced from 15.0% to 10.4%, while the rms scatter of the fractional redshift error does not change much.

[en] A recent analysis of cosmic ray air showers observed at the Pierre Auger Observatory indicates that nearby starburst galaxies (SBGs) might be the cause of ∼10% of the Ultra-High-Energy Cosmic Ray flux at energies E > 39 EeV . Since high energy neutrinos are a direct product of cosmic ray interactions, we investigate SBGs as a possible source of some of the ∼ 10⁻²–1 PeV neutrinos observed at IceCube. A statistical analysis is performed to establish the degree of positional correlation between the observed neutrinos and a set of 45 nearby radio- and infrared-bright SBGs. Our results are consistent with no causal correlation. However, a scenario where ∼ 10% of the High Energy Starting Events (HESE) in the detector are coming from the candidate SBGs is not excluded. The same conclusion is reached for different data subsets, as well as two different subsets of SBGs motivated by the Pierre Auger Observatory analysis.

[en] We combine wide and deep galaxy number-count data from the Galaxy And Mass Assembly, COSMOS/G10, Hubble Space Telescope (HST) Early Release Science, HST UVUDF, and various near-, mid-, and far-IR data sets from ESO, Spitzer, and Herschel. The combined data range from the far UV (0.15 μm) to far-IR (500 μm), and in all cases the contribution to the integrated galaxy light (IGL) of successively fainter galaxies converges. Using a simple spline fit, we derive the IGL and the extrapolated IGL in all bands. We argue that undetected low-surface-brightness galaxies and intracluster/group light are modest, and that our extrapolated-IGL measurements are an accurate representation of the extragalactic background light (EBL). Our data agree with most earlier IGL estimates and with direct measurements in the far IR, but disagree strongly with direct estimates in the optical. Close agreement between our results and recent very high-energy experiments (H.E.S.S. and MAGIC) suggests that there may be an additional foreground affecting the direct estimates. The most likely culprit could be the adopted model of zodiacal light. Finally we use a modified version of the two-component model to integrate the EBL and obtain measurements of the cosmic optical background (COB) and cosmic infrared background of ${24}_{-<!--\; ???\; -->4}^{+4}$ nW m⁻² sr⁻¹ and ${26}_{-<!--\; ???\; -->5}^{+5}$ nW m⁻² sr⁻¹ respectively (48%:52%). Over the next decade, upcoming space missions such as Euclid and the Wide Field Infrared Space Telescope will have the capacity to reduce the COB error to <1%, at which point comparisons to the very high-energy data could have the potential to provide a direct detection and measurement of the reionization field.

[en] Ultraviolet, optical and near-infrared images of the nearby (D ∼ 5.5 Mpc) SBm galaxy NGC 1311, obtained with the Hubble Space Telescope, reveal a small population of 13 candidate star clusters. We identify candidate star clusters based on a combination of their luminosity, extent, and spectral energy distribution. The masses of the cluster candidates range from ∼10³ M_sun up to ∼10⁵ M_sun, and show a strong positive trend of larger mass with increasing with cluster age. Such a trend follows from the fading and dissolution of old, low-mass clusters, and the lack of any young super-star clusters of the sort often formed in strong starbursts. The cluster age distribution is consistent with a bursting mode of cluster formation, with active episodes of age ∼10 Myr, ∼100 Myr, and ∼>Gyr. The ranges of age and mass we probe are consistent with those of the star clusters found in quiescent Local Group dwarf galaxies.

[en] We study six luminous Lyα emitters (LAEs) with very blue rest-frame UV continua at 5.7 ≤ z ≤ 6.6. These LAEs have previous Hubble Space Telescope (HST) and Spitzer IRAC observations. Combining our newly acquired HST images, we find that their UV-continuum slopes β are in a range of −3.4 ≤ β ≤ −2.6. Unlike previous, tentative detections of β ≃ −3 in photometrically selected, low-luminosity galaxies, our LAEs are spectroscopically confirmed and luminous (M _UV < −20 mag). We model their broadband spectral energy distributions (SEDs), and find that two β ≃ −2.6 ± 0.2 galaxies can be well fitted with young and dust-free stellar populations. However, it becomes increasingly difficult to fit bluer galaxies. We explore further interpretations by including the non-zero LyC escape fraction f _esc, very low metallicities, and/or active galactic nucleus contributions. Assuming f _esc ≃ 0.2, we achieve the bluest slopes β ≃ −2.7 when nebular emission is considered. This can nearly explain the SEDs of two galaxies with β ≃ −2.8 and −2.9 (σ _β = 0.15). Larger f _esc values and very low metallicities are not favored by the strong nebular line emission (evidenced by the IRAC flux) or the observed (IRAC 1 − IRAC 2) color. Finally, we find that the β ≃ −2.9 galaxy can potentially be well explained by the combination of a very young population with a high f _esc (≥0.5) and an old, dusty population. We are not able to produce two β ≃ −3.4 ± 0.4 galaxies. Future deep spectroscopic observations are needed to fully understand these galaxies.

[en] We present a reverberation mapping (RM) experiment that combines broad- and intermediate-band photometry; it is the first such attempt targeting 13 quasars at 0.2 < z < 0.9. The quasars were selected to have strong Hα or Hβ emission lines that are located in one of three intermediate bands (with FWHM around 200 Å) centered at 8045, 8505, and 9171 Å. The imaging observations were carried out in the intermediate bands and the broad i and z bands using the prime-focus imager 90Prime on the 2.3 m Bok telescope. Because of the large (∼1 deg"2) field of view (FOV) of 90Prime, we included the 13 quasars within only five telescope pointings or fields. The five fields were repeatedly observed over 20–30 epochs that were unevenly distributed over a duration of 5–6 months. The combination of the broad- and intermediate-band photometry allows us to derive accurate light curves for both optical continuum emission (from the accretion disk) and line emission (from the broad-line region, or BLR). We detect Hα time lags between the continuum and line emission in six quasars. These quasars are at relatively low redshifts 0.2 < z < 0.4. The measured lags are consistent with the current BLR size–luminosity relation for Hβ at z < 0.3. While this experiment appears successful in detecting lags of the bright Hα line, further investigation is required to see if it can also be applied to the fainter Hβ line for quasars at higher redshifts. Finally we demonstrate that, by using a small telescope with a large FOV, intermediate-band photometric RM can be efficiently executed for a large sample of quasars at z > 0.2