James Webb Space Telescope

SED template (top) and cutouts (bottom) of the candidate galaxy at z=12 (Rodighiero et al. 2023)

Redshift, stellar mass and dust extinction of the 2 μm-dropouts (coloured points, Bisigello et al. accepted). The majority are dusty dwarf galaxies at z<2.

The James Webb Space Telescope (JWST) is 6.5m space telescope passively cooled that will allow us to observe galaxies from the optical to the mid-IR up to very high redshifts. He has four instruments on board with imaging and spectroscopic capability betwee 0.6 and 28 μm.

We had a look of one of the first JWST observations centred on the SMACS0723 cluster and in the EGS field. We searched for 2 μm-dropouts, i.e. galaxies not visible at 2 μm but observed at longer wavelengths, and found a variety of dusty (active and passive) galaxies including 1) an intriguing candidate galaxy at z=12, 2) a passive and very dusty galaxy at z=5, and 3) a puzzling and unexpected population of very dusty dwarf galaxies at z<2!

Are you curious? These results have been published in two papers:

I am a junior member of the JWST Cosmic Evolution Early Release Science Survey and you can find all our publications here!

The JWST's blank galaxy survey will be mainly based on data provided by the two imaging cameras, the Near-Infrared Camera (NIRCam) at 0.6-5.0 μm and the Mid Infrared Instrument (MIRI) at λ>5.0 μm. Therefore, we analysed the quality of some galaxy properties, i.e. photometric redshift, stellar mass, age, colour excess and specific star formation rate, derived by using different combinations of NIRCam and MIRI broad band filters to careful prepare observational strategies.

The main results are:

- Observations at λ>0.6 μm are necessary to have the fraction of low-z contaminants under control at z<5
- Adding MIRI (F560W and F770W) photometry to the NIRCam data mitigates the absence of observations at λ>0.6 μm
- At z=7-10 a NIRCam photometry are adeguate for a correct photometric redshift recovery, but MIRI data help to improve the redshift estimation of red sources
- The presence of multiple nebular emission lines makes the photometric redshift and stellar mass recovery difficult
- At z=10, MIRI data are essential to recover proper stellar masses.

All the details are in these three papers:

"The impact of JWST broadband filter choice on photometric redshift estimation", L.Bisigello et al. 2016, ApJS,227,19B
"Recovering the Properties of High-redshift Galaxies with Different JWST Broadband Filters", L.Bisigello et al. 2017,ApJS,231,3B
"Statistical Stellar Mass Corrections for High-z Galaxies Observed with JWST Broadband Filters Due to Template Degeneracies",L.Bisigello et al. 2019,ApJS,243,27B

Examples of z=7, 8, 9 and 10 galaxy spectra. In background the wavelength coverage of some JWST broad-band filters.

Redshift recovery using only 8 NIRCam broad-band filters.

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