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1 @GTC We are proposing a new generation spectro-imager called BATMAN for GTC. This novel instrument is based on MOEMS (Micro-Opto-Electro-Mechanical Systems) programmable slit masks for multi-objectt spectroscopy (MOS). MOS is used extensively y to acquire the light fromm thousandss of astronomical targets simultaneously, to perform massive spectroscopic surveys, which are fundamental in astrophysics and cosmology, as they can address new fundamental knowledge in many different science topics. BATMAN optimises the Signal-to-Noisand background level occurring in slit-less spectroscopy is cancelled, as well as it provides higher throughput as compared to classical MOS using multi-slits. Fainter limiting l fluxes are reached and the scientific return is maximized both in cosmology, in galaxies formation and evolution, in stellar physics and in solar system small bodies characterization. A very relevant feature of BATMAN is that provides simultaneously imagingg of the same MOS field. Ratio (SNR): high precision spectra are obtained o andd the problem of spectral confusion 1- Science Drivers There is a very wide range of science cases that can be addressed with an instrument such BATMAN at GTC, below we highlight a number of topics that will make this facility unique. u High-redshift studies: Strong lensing science Ly-alpha extended emission (cosmicc web) at z=6-7 Study of galaxy clusters at z>1 Spectroscopic Deep Field Survey Nearby galaxies: Low surface brightness galaxies Extragalactic Planetary Nebula Deep survey of young stellar clusters in nearby galaxies g Star formation regions study using an adaptable slit Stellar Physics: Characterization of the stellar conten in open clusters The EHB (Extreme Horizontal Branch) stars study in globular clusters Near Earth Objects: : Detection and characterization - Spectroscopic Deep Field Survey One of the most exciting capability of our instrument would be to gather large representativee samples of galaxies from the locall Universe out to z~7. Such instrument could allow a a census of the most massive galaxies at z~6-8 at their cosmic dawn; then we would follow their evolution overr cosmic time with large and representative samples of galaxies at the peak of their activity. With such instrument observing simultaneously galaxies over a field-of-view of 36 arcmin 2 (option2), we could virtually observe all galaxies existing in the field-of-view at magnitude brighter than 25, which could be determinant to: 1) Trace the large-scalee structures at z>1. We could systematically identify proto-clusters, 2) perform detailed analysis of the galaxy metallicities, SFRs, and star-formation history using the good S/N spectra over a large period of cosmicc time; reconstruct the cosmic web, link galaxy evolution with their associated dark matter halos; 3) Characterize systematically the galaxy evolution with representativee sample. A complete spectroscopicc follow-up of all galaxies in fields like CANDELS survey is plausible. This could be a key to characterize the stellar masss assembly and the link between blackk holes and galaxy evolution.

2 - Lyman-α extended emission (cosmic web) at z= =6-7 The very recent MUSE/VLT discovery of extended Lyman-α emission from hydrogen around high-redshift galaxies has revealed that low surface brightness Lyman-α emission surrounding faint galaxiess at redshiftss between 3 and 6 adds up to a projected sky coverage of nearly 100% (Wisotzki( et al. 2018). BATMAN at GTC will offer an unique opportunity to study the IGM in Lyman-α at z~6-7 to detect the cosmic web in emission thanks to its large FOV (36( arcmin 2, Option 2) by combining its ability of a MOS and IFU-like mode and its superb imaging quality and larger GTC aperture. - Extragalactic Planetary Nebula There are a few dozen nearby galaxies where a number of PN have beenn detected, from dozens to t more than a thousand. They are very useful to study dynamics of galaxies, becausee they extend far out into the galaxy halo. They are also key in abundance determination becausee spectroscopic observations of planetary nebulaee are presently the only way to measure the chemical abundances of o individual elements in old and intermediatee age stars at distances of ~1Mpc orr greater. Last but not least, the luminosity function of PN is now well known to be an excellent standard candle in early type and in the bulges of spiral galaxies. The BATMAN MOS mode (option 2) at GTC will make a very relevant contributionn in this field. - Low Surface Brightness galaxies Low Surface Brightness galaxies (LSBs)( could represent a large fraction of local galaxies (up to 50% according to O Neil & Bothun 2000). They offer original tests for the determination of the Dark Matter content (Pickering et al. 1997). In the last decade, giant LSBs like Malin 1 have been revisited (Boissier et al. 2008, 2016, Galaz et al. 2016), LSB regionss have been found surrounding 30% % of nearby disk galaxies (Thilker et al. 2007): the so called extended UV galaxies (XUV), changing the paradigm on radial thresholdss for star formation (Boissier et al. 2007). Thousands (e.g. Koda et al. 2015) of galaxies of a completely new category (Ultra Diffuse Galaxies, UDGs) have been found owing to particular efforts to observed the diffuse sky, with original approach like the Dragonfly telescopee (van Dokkum et al., 2015). Some of thesee phenomena may be related, e.g. giant LSBs may be the most extreme cases of XUVV disks, LSBs and UDGs may share a common origin in large angular momentum (Boissier et al. 2003, Amorisco & Loeb 2016) but other assumptions have been discussed (e.g. forming UDGs by puffing out disks with outflows,, di Cintio et al. 2017). The origin of giant LSBs is still basically unknown: large spin s disks (e.g. Boissier et al. 2003, 2016), the results of head-on collisions (Mapelli et al. 2008), or large angular momentum late gas accretion (Stewart et al. 2017). Interactions may play a role in triggering the cooling of largee amount of halo gas, as suggested by the finding of a Malin 1 analoguee in Illustris-TNG (Zhu et al. 2018) ). Their exceedingly low surface brightness has been hindering in-depth studies of this important population. p New constraints are necessary to answer the current issues, especially concerning thee origin and evolution of this low surface brightness universe. Currently, spectroscopy is largely missing, with important questionss for all the categories of galaxies (e.g. metallicity of giant LSBs, a tracee of their history, distance of UDGs. For instance, the archetype Malin 1 for giant LSBs has relatively little spectroscopy. The emission lines in the giant disk have been measured only recently (Madathodika et al., in preparation), and only in a few regions, with long-slit spectrograph (IMACS Magellan). Especially for such galaxies, BATMAN at GTC will allow us to put slits in regions and structure where star formation is suspected (e.g. from blue UV colors). We shall be able to enlarge the slits inn the less favorable cases in order to maximize the chance of detecting Hα emission. Once line-emission iss secured, we should be b able to revisit the regions r with confirmed detection with a narrower slit in order to increase the spectral resolution. This should make us significant progress by constraining e.g. the very recent star formation rate of giant LSBs, but also the metallicity, the dust distribution in these unknown regions (this can bee done using g classical emission lines associated to star forming regions: Balmer lines, oxygen lines, [NII] lines, etc). Malin 1, the prototypical giant LSB is about circular with a 2 arcmin diameter, allowing to fit most m of the galaxy in one exposure. Several giant LSBs present similar properties and may be targeted. Similar argument applies to the XUV regions found in 30% of nearby galaxies.

3 - Young massive star clusters Studying young massive clusters offers a unique opportunity to accurately constrain stellar evolution. It allows to reducing the number and range of parameters (metallicity, age, rotation...) playing a role in this evolution, since for a given cluster, metallicity is the same for all members and populations are coeval. This is a crucial undertaking in order to pin down the cluster' s star-formation history,, the minimum mass of evolved objects and their nature. Thanks to the collecting power of GTC, and BATMAN'ss very good sensitivity, we would easily reach completeness s down to magnitudes correspondingg to the low-mass regimee of most clusters in the Galaxy. At R=4000, BATMAN delivers enough average resolving power to perform detailed spectral modelling, from which it is possible obtain wind andd stellar parameters, including stellar masses for the whole stellar population. This will ultimately allow to distinguish between competing scenario for the IMF (e.g. Weidner& Kroupa 2006; Parker & Goodwin 2007). Furthermore, BATMAN makes it easy to extract the spectra of the diffuse matter in clusters, hence to derivee the ionization parameters, abundances and kinematics. This will provide a comprehensive view of stellar feedback at work in such regions. We stress that with the collecting power of GTC, the (massive) stellar content of open clusters in Local Group galaxies becomes accessible, which means extending the studies described above to sub-solamagnitudes correspondin ng to the A0 spectral typee on the main-sequence, which is the low-mass end of the massive stars regime. r We note however that seeingg limited spatial resolution studies in Local Group galaxies subtends a field-of-viewf w with physical size of several parsecs, hence the risk of confusion cannot be neglected for meaningful statistical studies. metallicities. Indeed, for most of these galaxies, we could reach completeness down to 2- Instrument Concept We are proposing to develop a micro-mirror array based instrument: a two-arm system providing in parallell imaging and spectroscopic capabilities (see Fig.. 1). The micro-mirror array (MMA)) will provide a real-timee reconfigurable reflectivee slit-mask at the entrance of the spectrograph. This T MMA could be either a Digital- Micromirror-Device-based (DMD)) from Texas instruments composed of 2048x1080 micro-mirrors (13.68µm pitch) or a European-based micro-mirror array called MIRA (French-Swiss LAM-CSEM project) where the number as well as size off the micro-mirrors could be adaptedd to the dedicated BATMAN@GTC. The former MMA will lead to a limited FOV off 2.3x1.2 arcmin 2. The later will alloww a much larger FOV of 6x6 arcmin 2, or even more. The wavelength range goes from the UV/visible to the near-infrared, from 365 nm to 1000 nm. The spectral resolution would range from R=500 to 4000 for slits. See Table 1 for a summary of the instrument parameters. Thanks to its compact design, a high throughput is expected for BATMAN at GTC. The Imaging arm willl use multi-band filters and the Spectroscopic MOS multiplexing performance couldd reach several hundredd objects simultaneously and a sequential IFU may have any FOV from 1 up to thee whole F.O.V. The two arms are mounted on a common bench, and an upper bench supports the detectors thanks to two independent hexapods. The stiffnesss of the instrument is guaranteed thanks to a box architecture linking both benches. The volume of BATMAN is 1.4x1.2x0.75 m 3, with a total mass of 400kg (see Fig. 1) in the DMD-based option; for the MIRA-option, a redesign has to be done. A similar instrument concept will be placed initially on the 3.6m Telescopio Nazionale Galileo (TNG)( in La Palma by Mounting of all sub-systems has been done and integration of the individual arms is under way at LAM. The commissioning of BATMANN at GTC is of prime importance for characterizing the actual performance of this new family of MOS instruments, as well as investigating the neww operational procedures on astronomical objects (combining MOS and IFU modes, different spatial and spectral resolutions in the same FOV, absolute (spectro) photometry by combining imaging and spectroscopy y in the same instrument, automatic detection of transients ). The plan is to move this optimized instrument to Gemini in 2022 to benefit from a larger telescope diameter as welll as unique abilities of its Adaptive Optics System. Here, we are proposing to revisit in parallel our spectro-imager concept in order to develop a BATMAN for GTC, to be ready by 2025.

4 IFM IM2 SGR SFM TM4 TFP IM3 RL1 RL2 IM1 RTR SM1 SM3 RFM Z Light Beam direction (a) Y (b) Figure 1: Optical (a) and opto-mechanical (b) design of BATMANN Table 1: key numbers Telescope Primary mirror diameter F# Plate scale Option 1: DMD based BATMAN Field of view Focal ratio Wavelength range Spectral resolution Two arms instrument Detectors Option 2: MIRA based BATMAN Field of view Focal ratio Wavelength range Spectral resolution Two arms instrument Detectors GTC 10.4 m f/ µm/arcsec 2.3 x 1.2 arcmin 2 f/4 on DMD (with micro-mirrors, 13.68µm pitch) Plate scale = / micromirror / detector pixel nm R= for slit one spectroscopic channel and one imaging channel Two 2k x 6k CCDs 6 x 6 arcmin 2 f/16.33 on MIRA (with micro-mirrors, 82µm pitch) Plate scale = 0.1 / micromirror m / detector pixel nm R= for slit one spectroscopic channel and one imaging channel Two 4k x 8k CCDs

5 3- International context in 2019 in 2022 in 2025 (fully redesigned for GTC) 4- Budget and timeline We estimate a cost of 10M for completion in 6 years. 5- Team (preliminary list, under completion for further development) LAM, France: Frederic Zamkotsian,, Eric Jullo, Carlo Schimd, Olivier Ilbert, Sylvain de la Torre, Samuel Boissier, Jean-Claude Bouret, Georges Comte, Delphine Russeil, Audrey Delsanti, Pierre Vernazza, Benoit Neichel, Alessandro Boselli, Benoit Epinat, Philippe Amram, Romain Thomas, and Julienn Zoubian IAA-CSIC, Spain: Francisco Prada, Justo Sánchez, and Enrique Pérez References High-redshift studies Madau, Piero; Dickinson, Mark, 2014, Cosmic Star-Formation History, A&A M Ilbert et al., 2013, Mass assembly in quiescent and star-forming galaxies since z 4 from UltraVISTA, A& &A. 556A.55I Davidzon 2017, The COSMOS2015 galaxy stellar mass function. Thirteen billion years of stellar mass assembly in ten snapshots, A&A...605A..70D Grogin, N. A. et al., 2011, CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, ApJS, 197, 35 Wisotzki et al. 2018, arxiv: , Nearly all the sky is covered by Lyman-alpha emission around high redshift galaxies Nearby galaxies Madathodika, Boissier et al. (2019), in preparation: spectroscopy of Malin 1 Boissier et al. (2016), The properties of the Malin 1 galaxy giant disk: A panchromatic view from the NGVS and GUViCS surveys, A&A, 593, A126 Boissier (2016), The spectacular 200 kpc-wide disk of the Malin 1 giant low surface brightness galaxy, Proceedings of the International Astronomical Union, Volume 11, Issue S321 Boissier et al. (2008), GALEX Observations of Low Surface Brightness Galaxies: UV Color and Star Formation Efficiency, ApJ 681, 244 Stellar physics Weidner& Kroupa 2006, The maximumm stellar mass,, star-cluster formation and composite stellar populations, MNRAS, 365, 1333 Parker & Goodwin 2007, Do O-stars form in isolation?, MNRAS, 380, 1271 Instrumentation F. Zamkotsian, P. Lanzoni, E. Grassi,, R. Barette, C. Fabron, K. Tangen, L.. Valenziano, L. Marchand, L. Duvet " Successful evaluation for space applications of thee 2048x1080 DMD," in Proceedings P of the SPIE conference c on MOEMS 2011, Proc. SPIE 7932, San Francisco, USAA (2011) M. Canonica, F. Zamkotsian, P. Lanzoni, W. Noell, N. de Rooij, The two-dimensional array of 2048 tilting micromirrors for astronomical spectroscopy, Journal of Micromechanics and MicroengineeriM ing, , (2013) F. Zamkotsian, Michael Canonica, Patrick Lanzoni, Wilfried Noell, Sebastien Lani, " Large array off 2048 tilting micromirrors for astronomical spectroscopy: optical and cryogenic characterization", Proceedings of the SPIE conference on MOEMS 2014, Proc. SPIE 8977, San Francisco, USA (2014) Frederic Zamkotsian, Patrick Lanzoni, Nicolas Tchoubaklian, Harald Ramarijaona, Manuele Moschetti, Marco Riva, Marc Jaquet, Paolo Spano, William Bon, Mathieu Vachey, Luciano Nicastro, Emilio Molinari, Rosario Cosentino, Adriano Ghedina, Manuel Gonzalez, Walter Boschin, Paolo Di Marcantonio, Igor Coretti, Roberto Cirami, Filippo Zerbi, Luca Valenziano, TNG: Instrument integration and performance", inn Proceedingss of the SPIE conference on Astronomical Instrumentation 2018, Proc. SPIE 10702, Austin, USA, U (2018)