Max Gronke

High-resolution spectroscopy of a young, low-metallicity optically-thin L = 0.02L* star-forming galaxy at z = 3.12

We present VLT/X-Shooter and MUSE spectroscopy of a faint F814W = 28.60 +/- 0.33 (M-UV = -17.0), low-mass (less than or similar to 10(7)M(circle dot)), and compact (R-eff = 62 pc) freshly star-forming galaxy at z = 3.1169 magnified (16x) by the Hubble Frontier Fields galaxy cluster Abell S1063. Gravitational lensing allows for a significant jump toward lowluminosity regimes, in moderately high-resolution spectroscopy (R = lambda/d lambda similar to 3000-7400). We measured C IV lambda 1548, 1550, He II lambda 1640, OIII] lambda 1661, 1666, CIII]lambda lambda 1907, 1909, H beta, [O III] lambda lambda 4959, 5007 emission lines with FWHM less than or similar to 50 km s(-1) and (de-lensed) fluxes spanning the interval 1.0 x 10(-19)-2 x 10(-18) erg s(-1) cm(-2) at signal-to-noise ratio (S/N) = 4-30. The double-peaked Ly alpha emission with Delta v(red -blue) = 280(+/- 7) km s(-1) and delensed fluxes 2.4((blue))vertical bar 8.5((red)) x 10(-18) erg s(-1) cm(-2) (S/N = 38((blue))vertical bar 110((red)) indicate a low column density of neutral hydrogen gas consistent with a highly ionized interstellar medium as also inferred from the large [O III]lambda 5007/[O II] lambda 3727 > 10 ratio. We detect C IV lambda 1548, 1550 resonant doublet in emission, each component with FWHM less than or similar to 45 km s(-1) and redshifted by + 51(+/- 10) km s(-1) relative to the systemic redshift. We interpret this as nebular emission tracing an expanding optically thin interstellar medium. Both C IV lambda 1548, 1550 and He II lambda 1640 suggest the presence of hot and massive stars (with a possible faint active galactic nucleus). The ultraviolet slope is remarkably blue, beta = -2.95 +/- 0.20 (F-lambda = lambda(beta)), consistent with a dust-free and young less than or similar to 20 Myr galaxy. Line ratios suggest an oxygen abundance 12 + log(O/H) < 7.8. We are witnessing an early episode of star formation in which a relatively low N-H I and negligible dust attenuation might favor a leakage of ionizing radiation. This galaxy currently represents a unique low-luminosity reference object for future studies of the reionization epoch with the James Webb Space Telescope.

MUSE integral-field spectroscopy towards the Frontier Fields cluster Abell S1063: II. Properties of low luminosity Lyman α emitters at z > 3

In spite of their conjectured importance for the Epoch of Reionization, the properties of low-mass galaxies are currently still very much under debate. In this article, we study the stellar and gaseous properties of faint, low-mass galaxies at z > 3. We observed the Frontier Fields cluster Abell S1063 with MUSE over a 2 arcmin(2) field, and combined integral-field spectroscopy with gravitational lensing to perform a blind search for intrinsically faint Ly alpha emitters (LAEs). We determined in total the redshift of 172 galaxies of which 14 are lensed LAEs at z = 3-6.1. We increased the number of spectroscopically-confirmed multiple-image families from 6 to 17 and updated our gravitational-lensing model accordingly. The lensing-corrected Ly alpha luminosities are with L-Ly alpha less than or similar to 10(41.5) erg/s among the lowest for spectroscopically confirmed LAEs at any redshift. We used expanding gaseous shell models to fit the Ly alpha line profile, and find low column densities and expansion velocities. This is, to our knowledge, the first time that gaseous properties of such faint galaxies at z greater than or similar to 3 are reported. We performed SED modelling to broadband photometry from the U band through the infrared to determine the stellar properties of these LAEs. The stellar masses are very low (10(6-8) M-circle dot), and are accompanied by very young ages of 1-100 Myr. The very high specific star-formation rates (similar to 100 Gyr (-1)) are characteristic of starburst galaxies, and we find that most galaxies will double their stellar mass in less than or similar to 20 Myr. The UV-continuum slopes beta are low in our sample, with beta < -2 for all galaxies with M-star < 10(8) M-circle dot. We conclude that our low-mass galaxies at 3 < z < 6 are forming stars at higher rates when correcting for stellar mass effects than seen locally or in more massive galaxies. The young stellar populations with high star-formation rates and low HI column densities lead to continuum slopes and LyC-escape fractions expected for a scenario where low mass galaxies reionise the Universe.

Gravitational redshift profiles in the f(R) and symmetron models

Aims. We investigate the gravitational redshift in clusters of galaxies in the symmetron and Hu-Sawicky f (R) models. The characteristic feature of both models is the screening mechanism that hides the fifth force in dense environments recovering general relativity. Methods. We use N-body simulations that were run with the code Isis, which includes scalar fields, to analyse the deviation of observables in modified gravity models with respect to ΛCDM. Results. We find that the presence of the screening makes the deviation highly dependent on the halo mass. For instance, the f (R) parameters | fR0| = 10−5, n = 1 cause an enhancement of the gravitational signal by up to 50% for haloes with masses between 1013 M h−1 and 1014 M h−1. The characteristic mass range where the fifth force is most active varies with the model parameters. The usual assumption is that the presence of a fifth force leads to a deeper potential well and thus a stronger gravitational redshift. However, we find that in cases in which only the central regions of the haloes are screened, there could also be a weaker gravitational redshift.

Halo velocity profiles in screened modified gravity theories

Screened modified gravity predicts potentially large signatures in the peculiar velocity field that makes it an interesting probe to test gravity on cosmological scales. We investigate the signatures induced by the Symmetron and a Chameleon

Lyα Profile, Dust, and Prediction of Lyα Escape Fraction in Green Pea Galaxies

f(R)

Magnifying the Early Episodes of Star Formation: Super Star Clusters at Cosmological Distances

model in the peculiar velocity field using

FROM MIRRORS TO WINDOWS: LYMAN-ALPHA RADIATIVE TRANSFER IN A VERY CLUMPY MEDIUM

N

Connecting faint-end slopes of the Lyman α emitter and Lyman-break galaxy luminosity functions

-body simulations. By studying fifth force and halo velocity profiles we identify three general categories of effects found in screened modified gravity models: a fully screened regime where we recover

Universal predictions of screened modified gravity on cluster scales

\Lambda

Illuminating gas inflows/outflows in the MUSE deepest fields: Lyα nebulae around forming galaxies at z ≃ 3.3

CDM to high precision, an unscreened regime where the fifth force is in full operation, and, a partially screened regime where screening occurs in the inner part of a halo, but the fifth force is active at larger radii. These three regimes can be pointed out very clearly by analyzing the deviation in the maximum cluster velocity. Observationally, the partially screened regime is of particular interest since an uniform increase of the gravitational force - as present in the unscreened regime - is degenerate with the (dynamical) halo mass estimate, and, thus, hard to detect.