NGC 7457: Evidence for Merger-Driven Cylindrical Rotation in Disc the ﬁrst Ofﬁcial Application of the Schwpy Code!

NGC7457: A challenge to our understanding of the evolutionary mechanisms in disc galaxies

Alireza Molaeinezhad (IAC, Spain)

Dynamics Workshop, Vienna, 8 - 11 October 2019 Formation Theories for disc galaxies

Protogalactic Galaxy mergers, collapse Internal versus External RAM-pressure stripping of gas

star formation, gas recycling, metal enrichment, energy feedback via supernovae, etc. Fastversus Slow Fastversus Slow

Internal Internal versus External Environmental from Kormendy and Kennicutt (2004) Taken Secular evolution Secular evolution driven by bar instability, driven by prolongated gas infall, by dark matter haloes, by minor mergers, by spiral structures, by galaxy harassment, etc. etc. NGC7457: A peculiar low-mass lenticular galaxy in the ﬁlamentary group NGC 7331

NGC7457 is a highly inclined S0 galaxy (i = 74 deg) resides in one the 3 subgroups of ﬁlamentary group NGC 7331 (Ludwig et al. 2012). It is accompanied by UGC 12311, a spindle-shaped galaxy at a distance of 5.7′ from the centre of NGC 7457.

Parameter Value Source Distance (Mpc) 12.9 Alabi et al. (2017) Morphological type SA(rs)0-? de Vaucouleurs et al. (1991) PA (N–E) (deg.) 35 Molaeinezhad et al. (2016) Inclination (deg.) 74 Cappellari et al. (2013) Effective radius (arcsec) 32 de Vaucouleurs et al. (1991) Photometric bulge radii (xB , zB ) (arcsec) 11.0, 9.5 Molaeinezhad et al. (2016) M/L (Using HST/WFPC2 in the I–band) 1.86 Cappellari et al. (2006) V/σ (within 1Re ) 0.62 Cappellari et al. (2007) log(M∗ ) (M⊙ ) 10.13 Alabi et al. (2017) λRe (within 1Re ) 0.570 Cappellari et al. (2007) Gebhardt et al. (2003) MBH (M⊙) 3.5 × 106 StellarKinematics StellarPopulations Molaeinezhad et al. 2016, 2017, 2019 NGC7457: A peculiar low-mass lenticular galaxy in the ﬁlamentary group NGC 7331

The photometric, kinematics and stellar populations of this galaxy has been a matter of debate:

A very small bar-like distortion in the centre (Michard & Marchal 1994). No evidence in favour of a bar-like structure in this galaxy (Molaeinezhad et al. 2016). A signiﬁcantly high level of cylindrical rotation and unusually low measured velocity dispersion in the bulge (Silchenko et al. 2002; Emsellem et al. 2004; Molaeinezhad et al. 2016). A possible disc-like bulge on the basis of observed deviations from the Faber–Jackson L–σ relation (e.g. Kormendy 1993; Pinkney et al. 2003). Burstein (1979) classiﬁed this galaxy as a disc-dominated system with D/B = 1.6

Andredakis et al. (1995) argued the slope of luminosity proﬁle for bulges of this galaxy is much steeper (nSersic = 6) than one would expect for a disc-dominated galaxy, even steeper than namely normal lenticulars and of pure ellipticals.

Morphology and photometric features photometric and Morphology Erwin et al. (2015) claim that, the isophotal structure of this galaxy at both inner and outer regions could be very well described with a round classical bulge embedded within a highly inclined disc, with no evidence in favour of any bar-like stellar structure in the isophotes and surface brightness proﬁles.

A counter-rotating core (Sil’chenko et al. 2002, Molaeinezhad et al. 2016, 2019) A chemically distinct nuclei (r < 1. 5) younger than the surrounding bulge (Silchenko et al. 2002) associated with AGN (Gebhardt et al. 2003). populations and Kin. and populations

Considering the estimated halo assembly epoch of this galaxy, along with the low density environment of this system and discy distribution of its GCs, Zanatta et al. (2018) suggest a secular evolution scenario is the best mechanism to explain the observed properties of this system. Based on a detailed chromodynamical analysis of globular clusters (GCs) in this galaxy, Hargis et al. (2011) conclude that the formation scenario for this galaxy is most-likely through a merger event involving galaxies with unequal masses. 4 Formation scenarios Formation Cylindrical rotation in disc galaxies

Cylindrical rotation (Kormendy and Illingworth 1982) is an unusual kinematics feature, observed in B/P bulges.

Deﬁnition: lines of constant velocity are parallel to each other and perpendicular to the major axis. It means, within the bulge, the rotational velocity does not change with height:

∂ V/∂ |z| ~ 0

5 NGC7457: Very high level of cylindrical rotation with no BAR!!! -band image -band i Exponential disc subtracteddisc Exponential Line-of-sight (LOS) Velocity map and proﬁles mapand Velocity (LOS) Line-of-sight

The velocity map of NGC 7457 clearly exhibits a cylindrical rotation pattern within the photometric bulge region.

NGC 7457 has been classiﬁed as a SA0-(rs) (de Vaucouleurs et al. 1991) galaxy with no observational evidence supporting the presence of a B/P bulge or an strong bar in the photometric data.

The level of cylindrical rotation within the bulge dominated region is remarkably high (mcyl = 0.83 ± 0.06), even higher than that measured for strong B/P bulges in side-on bars with perfectly edge-on orientation!!!

Answering the question that ”What is the origin of such high level of cylindrical rotation in bulge of NGC7457?” could offer new insights into our understanding of the formation and evolution of this peculiar galaxy. 6 Schwarzschild’s orbit-superposition method

Schwarzschild’s (1979) orbit-superposition method is a powerful dynamical modelling technique that builds galactic models, using a representative library of stellar orbits in a gravitational potential and weighting them to reconstruct the observed surface brightness and kinematics of galaxies.

2D Multiple Gaussian Expansion Intrinsic shape param 2D image 3D triaxial MGE luminosity density space orientation of the galaxy Free param: p, q, u

Assume constant stellar M/L (Free Param)

Gravitational Potential + A spherical NFW halo + central BH mass (Free param) Intrinsic mass density model DM distribution Free param: C, M200 For all possible combination of free params: (p, q, u, M/L, M200, M_BH) Characterised orbits by r and λz λz Generating Orbits library Comparing orbit-superposition models Select orbits that admit E, I2, I3 With the observed SB and Kinematics

Find orbits weights Based on ρ (λz , r) Orbital decomposition (Based on λz) Best triaxial orbital model (cold, warm, hot and CR components)

Short-axis tube orbits Box orbits Inner-long axis tube orbits Modeled galaxy

+ + = The reconstructed kinematics map of the best orbital model for NGC7457 NGC7457: Orbital decomposition

Orbital Components:

1. Cold: 0.8 ︎ < λz ︎ < 1.0 (7 %) 2. Warm: 0.25 < λz < 0.8 (43 %) 3. Hot: −0.25 ︎ < λz ︎< 0.25 (46 %)

4. Counter rotating (CR): λz < −0.25 (< 4%) Califa data: Zhu et al. 2018 The reconstructed SB and kinematics maps of the orbital components

Cold component Remarkably high Sersic index and concentration (n=2.7, C=0.9) in the central parts. It cannot be ﬁt by a single Sersic proﬁle . It represents a perturbed disc with stars on nearly circular orbits. The reconstructed SB and kinematics maps of the orbital components

Warm component

Warm orbits contribute in both inner and outer parts of the surface brightness map. The SB proﬁle of the warm orbits are well described

by an exponential proﬁle (nSersic = 1.2), constitute a thick disc. The reconstructed SB and kinematics maps of the orbital components

Hot component Morphology: Elongated (and triaxial) spheroid. This orbital component with the highest contribution in the total luminosity of the best-fitting model, demonstrates significantly high level of Sersic index (n=3.6) and intrinsic flattening. The surface brightness of the hot component fairly matches the photometric bulge, with comparable scale length (∼ 10′′).

The reconstructed LOSVD map of this component shows clear rotation around the major photometric axis of this galaxy, known as ”prolate rotation” The reconstructed SB and kinematics maps of the orbital components

CR component The CR component of the best ﬁtting model is highly concentrated (C=1.4) in the central regions (r < 2. 5). The scale length of the CR component matches quite well the measured diameter of the KDC, observed in the centre of NGC 7457 (e.g. Emsellem et al. 2004). NGC 7457’s disc: born hot or dynamically heated?

Possible formation scenarios:

1. Disc stars were dynamically hot at birth (e.g. Bird et al. 2013). • Discs being formed originally thick in situ at high redshift by the merger of gas-rich protogalactic fragments and later thin discs may be formed. • This scenario should produce old stellar population in the thick disc, which is in contrast to the generally young population of stars, observed over the entire SAURON ﬁeld of NGC 7457!

2. Disc stars born in a very thin layer of gas with cold orbits and observed thickening have appeared more recently (e.g. Merrifield et al. 2001). • Stars were born dynamically cold in a primordially thin discs and can get dynamically heated and form a thick disc through different mechanisms e.g. satellite flybys, disturbances by satellite galaxies or mergers and secular thin disc flaring. • Given that, NGC 7457 is a relatively low-mass and dynamically young galaxy, any long-term secular scenario is unlikely. Moreover, there is no observational evidence in favour of possible progenitor of thick disc in our kinematical, chemical properties and dynamical modelling of this galaxy.

Comparing the velocity ellipsoid (σz /σR ) of the best-ﬁtting model for NGC 7457 and those predicted by the simulation studies, we suggest that the thick disc in NGC 7457 is most likely a dynamically heated structure, formed through the interactions and accretion of satellite(s) with near-polar initial inclinations (see Villalobos & Helmi (2008) For more details) Polar • • • Numerical and N-Body simulations suggest a gas-poor merger origin for systems these origin merger a gas-poor suggest simulations N-Body and Numerical understood. not well and debate under is still feature, its origin for this dynamical the rarity of Given observations or clusters groups to galaxy mostly belong galaxies, early-type few massive in observed been has This feature Merger

Tsatsi et al. (2017) Evidences in favour of the near-polar merger scenario

• NGC 7457 is located in a relatively low density environment (Ludwig et al. 2012) but still accretion or minor merger(s) in the past seem inevitable.

• Cold component of the best ﬁtting model for NGC 7457 represents a perturbed disc-like structure. It might be well the result of a (a near polar) merger perturbing the original (close to) exponential thin disc.

• Assuming the young stellar populations belong to the counter- rotating core of the gas-poor NGC 7457, known as KDC, gas is required to be present during the formation event. It is in favour of those formation scenario that involves a gas rich merger, but still strongly depends on the initial angular momentum of the acquired gas.

• Comparing the age of GCs (∼ 3-7 Gyr) and estimated halo assembly epoch of NGC 7457 (∼ 12.3 Gyr; Alabi et al. 2017) a gas-rich major merger is not the right mechanism to form these structures but still accretion and interaction of gas-rich satellite seem inevitable.

Duc et al. (2015) • As shown in Balcells & Gonzalez (1998), a disc-disc merger with mass ratio 3:1 or larger (intermediate mass ratio merger) does not destroy the orbital structure of the pre-existing disc, rather it heats it up leading to something resembling an S0, as a result of orbital redistribution. Cylindrical rotation in the absence of an strong bar

• Satellite encounters with an oblique impact angle of the satellite can disrupt the radial motion pattern of stars in host galaxies, boost the vertical motion of disc particles, and naturally help to diminish the vertical gradient in the LOSVD.

NGC 7457 could be considered as the ﬁrst evidence for merger-driven cylindrical rotation in the absence of a strong bar in disc galaxies. SchwPy Latest version: 1.2 (August 2019)

• SchwPy is a convenient interface to construct triaxial dynamical models of galaxies with a central black hole using Schwarzschild's (1979) orbital superposition approach.

• SchwPy is a line-by-line translation of the original IDL scripts (interface), developed by G. van den Ven and Ling Zhu.

• Unlike the IDL version, it is compatible to run on any HPC platform (SGE, SLURM, Condor, etc).

• It conducts all steps from the preparation of input data, over several analysis steps to the production of publication-quality plots.

• In contrast to previously presented IDL version, it is not specific to any specific setup and provides easy means of modification and further development, thanks to its modular code architecture. The code is clean and well-structured, making specific modifications by users easy and is designed to simplify the implementation of additional modules or modification of the existing analysis framework. Integrated Field Spectroscopy (IFU)

IFU Setup Data Cube IFU Spectroscopy IFU Internal Structure of bulges in disc galaxies

✦ Sample: 30 intermediate inclined disk galaxies from Balcells & Peletier (1993) sample. ✦ Method: IFU Spectroscopy (SAURON @ WHT) + Morphology study (HST & UKIRT)

Morphology Study of Bulges Stellar Kinematics of bulges Stellar populations of bulges

V-h3 correlation Correlation LevelCorrelation

Z_B

Molaeinezhad et al. 2016 Molaeinezhad et al. 2016 Molaeinezhad et al. 2017 MNRAS 456 (2016), 692-709 MNRAS 456 (2016), 692-709 MNRAS 467 (1) (2017), 353-368

✦ Sample: 30 intermediate inclined disk galaxies from Balcells & Peletier (1993) sample. ✦ Method: IFU Spectroscopy (SAURON @ WHT) + Morphology study (HST & UKIRT)

Morphology Study of Bulges Stellar Kinematics of bulges Stellar populations of bulges

V-h3 correlation Correlation LevelCorrelation

Z_B

Molaeinezhad et al. 2016 Molaeinezhad et al. 2016 Molaeinezhad et al. 2017 MNRAS 456 (2016), 692-709 MNRAS 456 (2016), 692-709 MNRAS 467 (1) (2017), 353-368

Collaborators: H.G. Khosroshahi (IPM, Iran), J. Falcon-Barroso (IAC, Spain), I. Martinez-Valpuesta (IAC, Spain), A. Vazdekis (IAC, Spain) , F. La Barbera (INAF, Italy) , R.F. Peletier (KAI, Netherlands) , M. Balcells (ING, Spain) A powerful dynamical modelling technique is the Schwarzschild’s (1979) orbit-superposition method, which builds galactic models by weighting the orbits generated in a gravitational potential. Short-axis tube orbits Box orbits Inner-long axis tube orbits Modeled galaxy

+ + =

Orbit dist. on the phase space of circularity Cumulative mass proﬁle NGC4210: The kinematics map (data and Model)

Total Mass

DISC

Bulge Stellar Mass

Circularity Bar

Dark Matter Mass NGC4210(Barred galaxy)

Collaborators: H.G. Khosroshahi (IPM, Iran), Ling Zhu (MPIA, Germany), Glenn van de Ven (ESO, Germany), J. Falcon-Barroso (IAC, Spain), R.F. Peletier (KAI, Netherlands) , M. Balcells (ING, Spain) Unveiling the hidden bars

Correlation of h3 and Velocity

Velocity h3 V-h3 correlation

X Correlation LevelCorrelation

NGC7332 (B/P bulge) NGC7332(B/P Z_B

23 Cylindrical rotation (Kormendy and Illingworth 1982) unusual kinematics feature, observed in B/P bulges.

Deﬁnition: lines of constant velocity are parallel to each other and perpendicular to the major axis. It means, within the bulge, the rotational velocity does not change with height:

∂ V/∂ |z| ~ 0

24 Cylindrical rotation in bulges

A new method to Quantify Cylindrical Rotation

Velocity Map Rotation 25 Curve Cyl. Rotation Level Vertical gradients of stellar populations in bulges What do the gradients tell us?

Unbarred bulges Barred bulges

Old stellar age Old stellar age

Negative Metallicity gradient Negative Metallicity gradient

uniformly distribution of [Mg/Fe] Positive vertical gradients of [Mg/Fe]

Pure merger-driven processes similar to low-luminosity ellipticals ? or Monolithic collapse ? (e.g. Moorthy & Holtzman 2006)

Bar buckling phase took place long time ago

Bulges form through merger of monolithically collapsed clouds at high redshifts (Baugh et al. 1996) Bars are long-lasting structures

26 that have been formed long time ago NGC7457: A Peculiar case

A classic bulge with a High level of Cylindrical rotation

No Bar or Fast rotation inner disk found !!

SDSS i band 2D V-h3 Correlation map velocity map

27 PhD work 1: Unveiling hidden bars on the basis of their kinematics see Molaeinezhad et al. 2016 for more details. Cylindrical rotation The rotational velocity does not change with height (∂ V/∂ |z| ∼ 0). We introduced a method to quantify cylindrical rotation that is robust against inner disc components.

V-h3 (anti)correlation We ﬁnd that the strong positive correlation between the stellar velocity (V ) and the h3 Gauss-Hermite parameter appears to be the most reliable indicator for the presence of bars. PhD work 2: The imprints of bars on the stellar population of bulges see Molaeinezhad et al. 2017 for more details.

Old bulges or old stars? Stellar AGE Stellar

Is it against the Secular evolution scenario? Metallicity

For bulges in barred systems:

Old stellar age (as old as unbarred bulges) + Positive vertical gradients of [Mg/Fe] [Mg/Fe] Bar buckling phase took place long time ago

Bars are long-lasting structures that have been formed long time ago NGC 7457: Evidence for merger-driven cylindrical rotation in disc The ﬁrst ofﬁcial application of the SCHWPy code!

• We construct Schwarzschild orbit-based models of NGC 7457, known as a peculiar low-mass lenticular galaxy. • Our best-fitting model successfully retrieves most of the unusual kinematics behaviours of this galaxy, in which, the orbital distribution of stars is dominated by warm and hot orbits. • By comparing our model with a variety of simulation studies, and considering the stellar kinematics and populations properties of this galaxy, we suggest that the thick disc is most likely a dynamically heated structure, formed through the interactions and accretion of satellite(s) with near- polar initial inclination. • We also suggest a merger-driven process as the most plausible scenario to explain the observed and dynamically-modelled properties of the bulge of NGC 7457. • We conclude that both the high level of cylindrical rotation and unusually low velocity dispersion reported for the NGC 7457 have most-likely external origins. • Therefore, NGC 7457 could be considered as a candidate for merger-driven cylindrical rotation in the absence of a strong bar in disc galaxies. NGC 7457: Evidence for merger-driven cylindrical rotation in disc The first official application of the SCHWPy code! 2018 to date: Advanced Processing System (APS) for the WEAVE project

The Advance Processing System (APS) is a software system that is part of the Science Processing and Archive (SPA) system. In particular, the APS is composed of speciﬁc science analysis tools allowing for the determination of astrophysical parameters relevant to the WEAVE main survey object classes. The APS extracts basic physical information from the fully reduced spectra (i.e. wavelength-calibrated, and sky-subtracted), produced by the Core Processing System (CPS) and makes this available for scientiﬁc exploitation.